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  • 1.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Halim, Joseph
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Näslund, Lars-Åke
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Chemical bonding in carbide MXene nanosheets2018Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, s. 27-32Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    tThe chemical bonding in the carbide core and the surface chemistry in a new group of transition-metalcarbides Tin+1Cn-Tx(n = 1,2) called MXenes have been investigated by surface-sensitive valence bandX-ray photoelectron spectroscopy. Changes in band structures of stacked nano sheets of different thick-nesses are analyzed in connection to known hybridization regions of TiC and TiO2that affect elastic andtransport properties. By employing high excitation energy, the photoelectron cross-section for the C 2s– Ti 3d hybridization region at the bottom of the valence band is enhanced. As shown in this work, theO 2p and F 2p bands strongly depend both on the bond lengths to the surface groups and the adsorptionsites. The effect of surface oxidation and Ar+sputtering on the electronic structure is also discussed.

    Publikationen är tillgänglig i fulltext från 2019-09-27 08:17
  • 2.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Tengdelius, Lina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Greczynski, Grzegorz
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Högberg, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    ­Chemical Bonding in Epitaxial ZrB2 Studied by X-ray Spectroscopy2018Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 649, s. 89-96Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The chemical bonding in an epitaxial ZrB2 film is investigated by Zr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies and compared to the ZrB2 compound target from which the film was synthesized as well as a bulk α-Zr reference. Quantitative analysis of X-ray Photoelectron Spectroscopy spectra reveals at the surface: ~5% O in the epitaxial ZrB2 film, ~19% O in the ZrB2 compound target and ~22% O in the bulk α-Zr reference after completed sputter cleaning. For the ZrB2 compound target, X-ray diffraction (XRD) shows weak but visible   11, 111, and 220 peaks from monoclinic ZrO2 together with peaks from ZrB2 and where the intensity distribution for the ZrB2 peaks show a randomly oriented target material.  For the bulk α-Zr reference no peaks from any crystalline oxide were visible in the diffractogram recorded from the 0001-oriented metal. The Zr K-edge absorption from the two ZrB2 samples demonstrate more pronounced oscillations for the epitaxial ZrB2 film than in the bulk ZrB2 attributed to the high atomic ordering within the columns of the film. The XANES exhibits no pre-peak due to lack of p-d hybridization in ZrB2, but with a chemical shift towards higher energy of 4 eV in the film and 6 eV for the bulk compared to α-Zr (17.993 keV) from the charge-transfer from Zr to B. The 2 eV larger shift in bulk ZrB2 material suggests higher oxygen content than in the epitaxial film, which is supported by XPS. In EXAFS, the modelled cell-edge in ZrB2 is slightly smaller in the thin film (a=3.165 Å, c=3.520 Å) in comparison to the bulk target material (a=3.175 Å, c=3.540 Å) while in hexagonal closest-packed metal (α-phase, a=3.254 Å, c=5.147 Å). The modelled coordination numbers show that the EXAFS spectra of the epitaxial ZrB2 film is highly anisotropic with strong in-plane contribution, while the bulk target material is more isotropic. The Zr-B distance in the film of 2.539 Å is in agreement with the calculated value from XRD data of 2.542 Å. This is slightly shorter compared to that in the ZrB2 compound target 2.599 Å, supporting the XANES results of a higher atomic order within the columns of the film compared to bulk ZrB2.

    Publikationen är tillgänglig i fulltext från 2020-03-06 14:13
  • 3.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Schmitt, Thorsten
    Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, Swiss Light Source (SLS), Switzerland.
    Duda, Laurent
    Department of Physics and Astronomy, Division of Molecular and Condensed Matter Physics, Uppsala University, Uppsala, Sweden.
    Polarization-dependent resonant inelastic X-ray scattering study atthe Cu L and O K-edges of YBa2Cu3O7-x2018Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, s. 38-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a study on the high-Tc superconductor (HTSC) YBa2Cu3O7-x(YBCO) using polarization-dependent X-ray absorption and resonant inelastic X-ray scattering. High-resolution measurementsusing synchrotron-radiation are compared with calculations using a quasi-atomic multiplet approachperformed at the Cu 2p3/2-edge of YBCO. We use a multiplet approach within the single impurity Ander-son model to reproduce and understand the character of the localized low-energy excitations in YBCO.We observe a distinct peak at about 0.5 eV in O K RIXS. This peak shows dependence on doping, incidentenergy, and momentum transfer that suggests that it has a different origin than the previously discussedcuprate bimagnons. Therefore, we assign it to bimagnon excitations within the Zhang Rice bands and/orthe Upper Hubbard bands, respectively.

    Publikationen är tillgänglig i fulltext från 2019-07-19 00:01
  • 4.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Fredrik
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Högberg, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Bonding Structures of ZrHx Thin Films by X-ray Spectroscopy2017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, s. 25750-25758Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The variation in local atomic structure and chemical bonding of ZrHx (x=0.15, 0.30, 1.16) magnetron sputtered thin films are investigated by Zr K-edge (1s) X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopies. A chemical shift of the Zr K-edge towards higher energy with increasing hydrogen content is observed due to charge-transfer and an ionic or polar covalent bonding component between the Zr 4d and the H 1s states with increasing valency for Zr. We find an increase in the Zr-Zr bond distance with increasing hydrogen content from 3.160 Å in the hexagonal closest-packed metal (a-phase) to 3.395 Å in the understoichiometric d-ZrHx film (CaF2-type structure) with x=1.16 that largely resembles that of bulk d-ZrH2. For yet lower hydrogen contents, the structures are mixed a- and d-phases, while sufficient hydrogen loading (x>1) yields a pure δ-phase that is understoichiometric, but thermodynamically stable. The change in the hydrogen content and strain is discussed in relation to the corresponding change of bond lengths, hybridizations, and trends in electrical resistivity.

    Publikationen är tillgänglig i fulltext från 2018-10-24 17:24
  • 5.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Mattesini, Maurizio
    Departamento de Física de la Tierra, Astronomía y Astrofísica I, , Madrid, Spain Instituto de Geociencias (CSIC-UCM), Facultad de CC. Físicas, Madrid, Spain.
    Chemical bonding and electronic-structure in MAX phases as viewed by X-ray spectroscopy and density functional theory2017Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 621, s. 108-130Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibit a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong M-C bonds in high-density MC slabs, and relatively weak M-A bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity, elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other materials properties makes it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.

    Publikationen är tillgänglig i fulltext från 2018-11-30 08:00
  • 6.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Schmidt, Susann
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Högberg, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Electronic properties and bonding in ZrHx thin films investigated by valence-bandx-ray photoelectron spectroscopy2017Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 96, nr 19, artikel-id 195103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure and chemical bonding in reactively magnetron sputtered ZrHx (x = 0.15, 0.30, 1.16)thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level,and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significantreduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H1s–Zr 4d hybridization region at ∼6 eV below the Fermi level. For low hydrogen content (x = 0.15, 0.30), thefilms consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ-ZrHx(CaF2-type structure) phases, while for x = 1.16, the films form single-phase ZrHx that largely resembles thatof stoichiometric δ-ZrH2 phase. We show that the cubic δ-ZrHx phase is metastable as thin film up to x = 1.16,while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated ZrH1.16film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4p3/2 and 3d5/2peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifiesa charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemicalshifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affectsthe conductivity by charge redistribution in the valence band.

  • 7.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Induced magnetism at the interfaces of a Fe/V superlattice investigated by resonant magnetic x-ray scattering2017Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 422, s. 362-366Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The induced magnetic moments in the V 3d electronic states of interface atomic layers in a Fe(6ML)/V(7ML) superlattice was investigated by x-ray resonant magnetic scattering. The first V atomic layer next to Fe was found to be strongly antiferromagnetically polarized relatively to Fe and the magnetic moments of the next few atomic layers in the interior V region decay exponentially with increasing distance from the interface, while the magnetic moments of the Fe atomic layers largely remain bulk-like. The induced V moments decay more rapidly as observed by x-ray magnetic scattering than in standard x-ray magnetic circular dichroism. The theoretical description of the induced magnetic atomic layer profile in V was found to strongly rely on the interface roughness within the superlattice period. These results provide new insight into interface magnetism by taking advantage of the enhanced depth sensitivity to the magnetic profile over a certain resonant energy bandwidth in the vicinity of the Bragg angles.

  • 8.
    Olovsson, Weine
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Alling, Björn
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Max-Planck-Institut für Eisenforschung GmbH, D-402 37 Düsseldorf, Germany.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Structure and Bonding in Amorphous Cr1−xCx Nanocomposite Thin Films: X‐ray Absorption Spectra and First-Principles Calculations2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 23, s. 12890-12899Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The local structure and chemical bonding in two-phase amorphous Cr1−xCx nanocomposite thin films are investigated by Cr K-edge (1s) X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies in comparison to theory. By utilizing the computationally efficient stochastic quenching (SQ) technique, we reveal the complexity of different Cr-sites in the transition metal carbides, highlighting the need for large scale averaging to obtain theoretical XANES and EXAFS spectra for comparison with measurements. As shown in this work, it is advantageous to use ab initio theory as an assessment to correctly model and fit experimental spectra and investigate the trends of bond lengths and coordination numbers in complex amorphous materials. With sufficient total carbon content (≥30 at. %), we find that the short-range coordination in the amorphous carbide phase exhibit similarities to that of a Cr7C3 ± y structure, while excessive carbons assemble in the amorphous carbon phase.

  • 9.
    Furlan, Andrej
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Jansson, Ulf
    Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Structure and bonding in amorphous iron carbide thin films2015Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, nr 4, s. 045002-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the amorphous structure, chemical bonding, and electrical properties ofmagnetron sputtered Fe1−xCx (0.21 < x < 0.72) thin films. X-ray, electron diffraction andtransmission electron microscopy show that the Fe1−xCx films are amorphousnanocomposites, consisting of a two-phase domain structure with Fe-rich carbidic FeCy , and acarbon-rich matrix. Pair distribution function analysis indicates a close-range order similar tothose of crystalline Fe3C carbides in all films with additional graphene-like structures at highcarbon content (71.8 at% C). From x-ray photoelectron spectroscopy measurements, we findthat the amorphous carbidic phase has a composition of 15–25 at% carbon that slightlyincreases with total carbon content. X-ray absorption spectra exhibit an increasing number ofunoccupied 3d states and a decreasing number of C 2p states as a function of carbon content.These changes signify a systematic redistribution in orbital occupation due to charge-transfereffects at the domain-size-dependent carbide/matrix interfaces. The four-point proberesistivity of the Fe1−xCx films increases exponentially with carbon content from ∼200μcm(x = 0.21) to ∼1200μcm (x = 0.72), and is found to depend on the total carbon contentrather than the composition of the carbide. Our findings open new possibilities for modifyingthe resistivity of amorphous thin film coatings based on transition metal carbides through thecontrol of amorphous domain structures.

  • 10.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Mattesini, Maurizio
    Departamento de F í sica de la Tierra, Astronom í a y Astrof í sica I, Universidad Complutense de Madrid, Madrid, Spain; Instituto de Geociencias (CSIC-UCM), Facultad de CC. F í sicas, Madrid, Spain.
    Bugnet, Mattieu
    Département de Physique et Mecanique des Matériaux, Institut Pprime, UPR 3346 CNRS: Université de Poitiers: ENSMA, SP2MI, Futuroscope, France; Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Département de Physique et Mecanique des Matériaux, Institut Pprime, UPR 3346 CNRS: Université de Poitiers: ENSMA, SP2MI, Futuroscope, France.
    The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft X-ray spectroscopy and ab initio calculations2015Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, nr 41, s. 415501-415509Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal di erences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L2;3, C K, and Ge M1, M2;3 emission spectra are interpreted with rst-principles density-functional theory (DFT) including core-tovalence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should a ect the thermal expansion coecient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.

  • 11.
    Furlan, Andrej
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Jansson, Ulf
    Uppsala University, Sweden .
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites2014Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, nr 41, s. 415501-415512Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni1−xCx (0.05≤x≤0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiCy phase), instead of the expected rhombohedral-Ni3C. At low carbon content (4.9 at%), the thin film consists of hcp-NiCy nanocrystallites mixed with a smaller amount of fcc-NiCx. The average grain size is about10–20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiCy nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiCy and fcc-NiCx nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp2 hybridization, consistent with photoelectron spectra that show a decreasing amount of C–Ni phase with increasing carbon content. The Ni 3d–C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show thatthe resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.

  • 12.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Schmitt, Thorsten
    Paul Scherrer Institut, Swiss Light Source (SLS), Villigen, Switzerland.
    Strocov, Vladimir
    Paul Scherrer Institut, Swiss Light Source (SLS), Villigen, Switzerland.
    Schlappa, Justina
    Paul Scherrer Institut, Swiss Light Source (SLS), Villigen, Switzerland.
    Kalabukhov, Alex
    Chalmers University of Technology, Gothenburg, Sweden.
    Duda, Laurent
    Uppsala University, Sweden.
    Self-doping processes between planes and chains in the metal-to-superconductor transition of YBa2Cu3O6.92014Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, nr 07017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interplay between the quasi 1-dimensional CuO-chains and the 2-dimensional CuO2 planes ofYBa2Cu3O61x (YBCO) has been in focus for a long time. Although the CuO-chains are known to beimportant as charge reservoirs that enable superconductivity for a range of oxygen doping levels in YBCO,the understanding of the dynamics of its temperature-driven metal-superconductor transition (MST)remains a challenge. We present a combined study using x-ray absorption spectroscopy and resonantinelastic x-ray scattering (RIXS) revealing how a reconstruction of the apical O(4)-derived interplanarorbitals during theMSTof optimally dopedYBCOleads to substantial hole-transfer from the chains into theplanes, i.e. self-doping. Our ionic model calculations show that localized divalent charge-transferconfigurations are expected to be abundant in the chains of YBCO. While these indeed appear in the RIXSspectra from YBCO in the normal, metallic, state, they are largely suppressed in the superconducting stateand, instead, signatures of Cu trivalent charge-transfer configurations in the planes become enhanced. Inthe quest for understanding the fundamental mechanism for high-Tc-superconductivity (HTSC) inperovskite cuprate materials, the observation of such an interplanar self-doping process in YBCO opens aunique novel channel for studying the dynamics of HTSC.

  • 13.
    Ritchie, Andrew
    et al.
    University of Saskatchewan, Saskatoon, SK, Canada.
    Eger, Shaylin
    University of Saskatchewan, Saskatoon, SK, Canada.
    Wright, Chelsey
    Canadian Light Source, Saskatoon, SK, Canada.
    Chelladurai, Saniel
    University of Saskatchewan, Saskatoon, SK, Canada.
    Borrowman, Cuyler
    University of Saskatchewan, Saskatoon, SK, Canada.
    Olovsson, Weine
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Verma, Jai
    University of Notre Dame, IN, USA.
    Jena, Debdeep
    Univeristy of Notre Dame, IN, USA.
    Grace Xing, Huili
    University of Notre Dame, IN, USA.
    Duboc, Christian
    Osemi Canada Inc., Sherbrooke, Quebec, Canada.
    Urquhart, Stephen
    University of Saskatchewan, Saskatoon, SK, Canada.
    Strain sensitivity in the nitrogen 1s NEXAFS spectra of gallium nitride2014Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 316, s. 232-236Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nitrogen 1s near edge X-ray absorption fine structure (NEXAFS) of gallium nitride (GaN) shows astrong natural linear dichroism that arises from its anisotropic wurtzite structure. An additional spectro-scopic variation arises from lattice strain in epitaxially grown GaN thin films. This variation is directlyproportional to the degree of strain for some spectroscopic features. This strain variation is interpretedwith the aid of density functional theory calculations.

  • 14.
    Halim, Joseph
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. Department of Materials Science & Engineering and 3A.J. Drexel Nanotechnology Institute, Drexel University, Philadelphia, USA.
    Cook, Kevin M.
    University of Penn, PA 19104 USA Drexel University, PA 19104 USA .
    Näslund, Lars-Åke
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. University of Penn, PA 19104 USA .
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Gogotsi, Yury
    University of Penn, PA 19104 USA Drexel University, PA 19104 USA .
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Rosén, Johanna
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Barsoum, Michel W.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. Department of Materials Science & Engineering, Drexel University, Philadelphia, USA.
    X-ray Photoelectron Spectroscopy Characterization of Two-Dimensional Titanium Metal Carbides (MXenes)2014Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Herein, we report X-ray Photoelectron Spectroscopy (XPS) analysis for cold pressed exfoliated 2D nanocrystals of transition metal carbides, MXenes. MXenes are a recently discovered family of 2D materials produced by selective chemical etching of the A element from MAX phases which are ternary metal carbides and nitrides. The latter has the formula of Mn+1AXn, where M is an early transition metal, A is an A-group element, and X is C and/or N. This study is a comparison between two MXenes, Ti3C2Tx and Ti2CTx, where Tx stands for surface termination groups such as –O, –OH, and –F. Ti3C2Tx and Ti2CTx were prepared by immersion of Ti3AlC2 and Ti2AlC powders in 50% conc. HF. A thorough XPS analysis was performed through peak fitting of high resolution XPS spectra and valence band, VB, spectra analysis. The effect of Ar sputtering as well as the number of layers n was the primarily interest of this study. According to the peak fitting analysis, both phases contain the following species, Ti–C, C–C, Ti–F, Ti–O and Ti–OH resulting in the following chemical formulas: Ti3C2(OH)x(O)y(F)z and Ti2C(OH)x(O)y(F)z. Comparing the VB spectra with the DOS calculations show the valance band spectra is actually a mixture of MXene with various terminations of OH, O and F. Before Ar+ sputtering both phases show a large percentage of fluorinated-TiO2 which is due to MXene surface oxidation as well as CHx, C-O and COO groups arising from either surface contaminations or due to drying the etched powders in ethanol after washing the powder of the HF acid. According to the VB spectra, it is shown that the fluorinated TiO2 is actually a mixture of anatase and rutile. The number of layers, n, also plays a role; the lower n, the more the MXene is prone to oxidation.

  • 15.
    Mattesini, Maurizio
    et al.
    Universidad Complutense de Madrid, Spain.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    Electronic correlation effects in the Cr2GeC Mn+1AXn phase2012Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 3, s. 035601-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The magnetic properties, electronic band structure and Fermi surfaces of the hexagonal Cr2GeC system have been studied by means of both generalized gradient approximation (GGA) and the +U corrected method (GGA + U). The effective U value has been computed within the augmented plane wave theoretical scheme by following the constrained density functional theory formalism of Anisimov and Gunnarsson (1991 Phys. Rev. B 45 7570–74). On the basis of our GGA + U calculations, a compensated antiferromagnetic spin ordering of Cr atoms has been found to be the ground-state solution for this material, where a Ge-mediated super-exchange coupling is responsible for an opposite spin distribution between the ABA stacked in-plane Cr–C networks. Structural properties have also been tested and found to be in good agreement with the available experimental data. Topological analysis of Fermi surfaces has been used to qualitatively address the electronic transport properties of Cr2GeC, and found an important asymmetrical carrier-type distribution within the hexagonal crystal lattice. We conclude that an appropriate description of the strongly correlated Cr d electrons is an essential issue for interpreting the material properties of this unusual Cr-based MAX phase.

  • 16.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Andersson, Matilda
    Uppsala University.
    Lu, Jun
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Jansson, Ulf
    Uppsala University.
    Electronic Structure and Chemical Bonding of AmorphousChromium Carbide Thin Films2012Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, s. 225004-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The microstructure, electronic structure, and chemical bonding of chromium carbidethin films with different carbon contents have been investigated with high-resolutiontransmission electron microscopy, electron energy loss spectroscopy and soft x-rayabsorption-emission spectroscopies. Most of the films can be described as amorphousnanocomposites with non-crystalline CrCx in an amorphous carbon matrix. At highcarbon contents, graphene-like structures are formed in the amorphous carbon matrix.At 47 at% carbon content, randomly oriented nanocrystallites are formed creating acomplex microstructure of three components. The soft x-ray absorption-emissionstudy shows additional peak structures exhibiting non-octahedral coordination andbonding.

  • 17.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Mattesini, Maurizio
    Universidad Complutense de Madrid.
    Van Nong, Ngo
    Technical University of Denmark.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Electronic-structure origin of the anisotropic thermopower of nanolaminated Ti3SiC2 determinedby polarized x-ray spectroscopy and Seebeck measurements2012Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 85, s. 195134-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanolaminated materials exhibit characteristic magnetic, mechanical, and thermoelectric properties, withlarge contemporary scientific and technological interest. Here we report on the anisotropic Seebeck coefficient innanolaminated Ti3SiC2 single-crystal thin films and trace the origin to anisotropies in element-specific electronicstates. In bulk polycrystalline form, Ti3SiC2 has a virtually zero Seebeck coefficient over a wide temperaturerange. In contrast, we find that the in-plane (basal ab) Seebeck coefficient of Ti3SiC2, measured on single-crystalfilms, has a substantial and positive value of 4–6 μV/K. Employing a combination of polarized angle-dependentx-ray spectroscopy and density functional theory we directly show electronic structure anisotropy in inherentlynanolaminated Ti3SiC2 single-crystal thin films as a model system. The density of Ti 3d and C 2p states atthe Fermi level in the basal ab plane is about 40% higher than along the c axis. The Seebeck coefficient isrelated to electron and hole-like bands close to the Fermi level, but in contrast to ground state density functionaltheory modeling, the electronic structure is also influenced by phonons that need to be taken into account.Positive contribution to the Seebeck coefficient of the element-specific electronic occupations in the basal planeis compensated by 73% enhanced Si 3d electronic states across the laminate plane that give rise to a negativeSeebeck coefficient in that direction. Strong phonon vibration modes with three to four times higher frequencyalong the c axis than along the basal ab plane also influence the electronic population and themeasured spectra bythe asymmetric average displacements of the Si atoms. These results constitute experimental evidence explainingwhy the average Seebeck coefficient of Ti3SiC2 in polycrystals is negligible over a wide temperature range. Thisallows the origin of anisotropy in physical properties of nanolaminated materials to be traced to anisotropies inelement-specific electronic states.

  • 18.
    Hahlin, Maria
    et al.
    Uppsala University.
    Odelius, M
    Stockholm University.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Johansson, Erik
    Uppsala University.
    Plogmaker, S
    Uppsala University.
    Hagberg, D
    Royal Institute of Technology.
    Sun, L
    Royal Institute of Technology.
    Siegbahn, H
    Royal Institute of Technology.
    Rensmo, H
    Uppsala University.
    Mapping the frontier electronic structures of triphenylamine basedorganic dyes at TiO2 interfaces2011Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 8, s. 3534-3546Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The frontier electronic structures of a series of organic dye molecules containing a triphenylaminemoiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated byphotoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emissionspectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental resultswere compared to electronic structure calculations on the molecules, which are used to confirmand enrich the assignment of the spectra. The approach allows us to experimentally measure andinterpret the basic valence energy level structure in the dye, including the highest occupied energylevel and how it depends on the interaction between the different units. Based on N 1s X-rayabsorption and emission spectra we also obtain insight into the structure of the excited states,the molecular orbital composition and dynamics. Together the results provide an experimentallydetermined energy level map useful in the design of these types of materials. Included are alsoresults indicating femtosecond charge redistribution at the dye/TiO2 interface.

  • 19.
    Mendoza-Galvan, Arturo
    et al.
    Cinvestav-Querétaro, Libramiento Norponiente.
    Rybka, M
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Järrendahl, Kenneth
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Arwin, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad optik. Linköpings universitet, Tekniska högskolan.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Barsoum, Michel
    Drexel University.
    Spectroscopic ellipsometry study on the dielectric function of bulk Ti2AlN,Ti2AlC, Nb2AlC, (Ti0.5,Nb0.5)2AlC, and Ti3GeC2 MAX-phases2011Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, s. 013530-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The averaged complex dielectric function =2+ /3 of polycrystalline Ti2AlN, Ti2AlC,Nb2AlC, Ti0.5,Nb0.52AlC, and Ti3GeC2 was determined by spectroscopic ellipsometry coveringthe mid infrared to the ultraviolet spectral range. The dielectric functions and correspond tothe perpendicular and parallel dielectric tensor components relative to the crystallographic c-axis ofthese hexagonal compounds. The optical response is represented by a dispersion model with Drude–Lorentz and critical point contributions. In the low energy range the electrical resistivity is obtainedfrom the Drude term and ranges from 0.48 m for Ti3GeC2 to 1.59 m for Ti0.5,Nb0.52AlC.Furthermore, several compositional dependent interband electronic transitions can be identified. Forthe most important ones, Im shows maxima at: 0.78, 1.23, 2.04, 2.48, and 3.78 eV for Ti2AlN;0.38, 1.8, 2.6, and 3.64 eV for Ti2AlC; 0.3, 0.92, and 2.8 eV in Nb2AlC; 0.45, 0.98, and 2.58 eV inTi0.5,Nb0.52AlC; and 0.8, 1.85, 2.25, and 3.02 eV in Ti3GeC2.

  • 20.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Mattesini, Maurizio
    Universidad Complutense de Madrid.
    Höglund, Carina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Electronic structure of GaN and Ga investigated by soft x-ray spectroscopy and first-principles methods2010Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, s. 085125-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure and chemical bonding of wurtzite-GaN investigated by N 1s soft x-ray absorption spectroscopy and N K, Ga M1, and Ga M2,3 emission spectroscopy is compared to that of pure Ga. The measurements are interpreted by calculated spectra using first-principles density-functional theory (DFT) including dipole transition matrix elements and additional on-site Coulomb interaction (WC-GGA+U). The Ga 4p-N 2p and Ga 4s-N 2p hybridization and chemical bond regions are identified at the top of the valence band between −1.0 and −2.0 and further down between −5.5 and −6.5 eV, respectively. In addition, N 2s-N 2p-Ga 4s and N 2s-N 2p-Ga 3d hybridization regions occur at the bottom of the valence band between −13 and −15 eV, and between −17.0 and −18.0 eV, respectively. A bandlike satellite feature is also found around −10 eV in the Ga M1 and Ga M2,3 emission from GaN, but is absent in pure Ga and the calculated ground-state spectra. The difference between the identified spectroscopic features of GaN and Ga are discussed in relation to the various hybridization regions calculated within band-structure methods.

  • 21.
    Mattesini, Maurizio
    et al.
    Universidad Complutense de Madrid.
    Magnuson, Martin
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Tasnádi, Ferenc
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Höglund, Carina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Abrikosov, Igor A.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Elastic properties and electrostructural correlations in ternary scandium-based cubic inverse perovskites: A first-principles study2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 125122Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wehave performed ab initio calculations for the cubic inverse-perovskite Sc3EN(E=Al,Ga,In) systems to study their electronic band-structures and elastic properties.In this study, we used the accurate augmented plane waveplus local orbital method to find the equilibrium structural parametersand to compute the full elastic tensors. The obtained single-crystalelastic constants were used to quantify the stiffness of theSc-based ternary nitrides and to appraise their mechanical stability. Thesite-projected density of states, Fermi surfaces, and the charge-density plotshave also been used to analyze the chemical bonding betweenthe Sc6N cluster and the surrounding metallic lattice of eitherAl, Ga, or In atoms. Our calculations show that Sc3GaNhas the largest covalent Sc-N bonding-type character with the highestYoung, shear, and bulk moduli. Compared with the other twoisoelectronic systems, it also behaves as the most brittle materialwith a relatively large elastic anisotropy.

  • 22.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Mattesini, M.
    Universidad Complutense de Madrid.
    Höglund, Carina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Electronic structure and chemical bonding anisotropy investigation of wurtzite AlN2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, s. 155105-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure and the anisotropy of the Al - N p and s chemical bonding of wurtzite AlN has been investigated by bulk-sensitive total fluorescence yield absorption and soft x-ray emission spectroscopies. The measured N K, Al L1, and Al L2,3 x-ray emission and N 1s x-ray absorption spectra are compared with calculated spectra using first principles density-functional theory including dipole transition matrix elements. The main N 2p - Al 3p hybridization regions are identified at -1.0 to -1.8 eV and -5.0 to -5.5 eV below the top of the valence band. In addition, N 2s - Al 3p and N 2s - Al 3s hybridization regions are found at the bottom of the valence band around -13.5 eV and -15 eV, respectively. A strongly modified spectral shape of Al 3s states in the Al L2,3 emission from AlN in comparison to Al metal is found, which is also reflected in the N 2p - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structure and chemical bonding of AlN and Al metal are discussed in relation to the position of the hybridization regions and the valence band edge influencing the magnitude of the large band gap.

  • 23.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Lewin, Erik
    Uppsala University.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Jansson, Ulf
    Uppsala University.
    Electronic structure and chemical bonding of nanocrystalline-TiC/amorphous-C nanocomposites2009Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, nr 235108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theelectronic structure of nanocrystalline (nc-) TiC/amorphous C nanocomposites has beeninvestigated by soft x-ray absorption and emission spectroscopy. The measuredspectra at the Ti 2p and C 1s thresholds of the nanocompositesare compared to those of Ti metal and amorphous C.The corresponding intensities of the electronic states for the valenceand conduction bands in the nanocomposites are shown to stronglydepend on the TiC carbide grain size. An increased chargetransfer between the Ti 3d-eg states and the C 2p states hasbeen identified as the grain size decreases, causing an increasedionicity of the TiC nanocrystallites. It is suggested that thecharge transfer occurs at the interface between the nanocrystalline-TiC andthe amorphous-C matrix and represents an interface bonding which maybe essential for the understanding of the properties of nc-TiC/amorphousC and similar nanocomposites.

  • 24.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Q-dependent RIXS investigation of low-energy excitations in single-crystal mixed valence manganese perovskites2009Rapport (Övrigt vetenskapligt)
  • 25.
    Mendoza-Galvan, Arturo
    et al.
    Cinvestav-Queretaro, Mexico.
    Rybka, Marcin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad optik. Linköpings universitet, Tekniska högskolan.
    Järrendahl, Kenneth
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad optik. Linköpings universitet, Tekniska högskolan.
    Arwin, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tillämpad optik. Linköpings universitet, Tekniska högskolan.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Barsoum, Michel
    Drexel University.
    Spectroscopic Ellipsometry of Bulk MAX-phases2009Ingår i: Proceedings of the AVS 56th International Symposium & Exhibition, 2009, 2009Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    MAX-phases are compounds with the chemical formula Mn+1AXn where M is a transition metal, A is an element from column 13 to 16 in the periodic system and X represents C or N and n = 1, 2 or 3. These materials are potentially technologically important as they show unique refractory and other physical properties due to the combination of metals and ceramics. From a fundamental point of view the band structure of these materials are of interest and optical reference data are important to determine. Herein we report, for the first time, on the optical properties of NbTiAlC, Nb2AlC, TiSC2, Cr2GeC, TiGeC2, Ti2AlC, and Ti2AlN by spectroscopic ellipsometry in the 0.03 to 6.0 eV spectral range. The ellipsometric data in the infrared range show features corresponding to Fano modes indicating the presence of a thin oxide layer a few nm thick. The optical response of these MAX-phases is represented by a Drude-Lorentz model. Thus, in the low energy range the electrical conductivity through the Drude term is evaluated and two or three interband electronic transitions which are compositional dependent can be identified at photon energies in the visible-ultraviolet range 1.0-6.0 eV.

  • 26.
    Magnuson, Martin
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Wilhelmsson, Ola
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Mattesini, Maurizio
    Departamento de Física de la Tierra, Astronomía y Astrofísica I, Universidad Complutense de Madrid.
    Li, Sa
    Department of Physics, Uppsala University.
    Ahuja, Rajeev
    Department of Physics, Uppsala University.
    Eriksson, Olle
    Department of Physics, Uppsala University.
    Högberg, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Jansson, Ulf
    Uppsala University.
    Anisotropy in the electronic structure of V2GeC investigated by soft x-ray emission spectroscopy and first-principles theory2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, nr 035117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theanisotropy of the electronic structure of ternary nanolaminate V2GeC isinvestigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependentemission spectra of V L2,3, C K, Ge M1, and Ge M2,3 in V2GeCare compared with those from monocarbide VC and pure Ge.The experimental emission spectra are interpreted with calculated spectra usingab initio density-functional theory including dipole transition matrix elements. Differenttypes of covalent chemical bond regions are revealed: V 3d-C 2p bondingat −3.8  eV, Ge 4p-C 2p bonding at −6  eV, and Ge 4p-C 2s interaction mediatedvia the V 3d orbitals at −11  eV below the Fermi level.We find that the anisotropic effects are high for the4p valence states and the shallow 3d core levels ofGe, while relatively small anisotropy is detected for the V 3dstates. The macroscopic properties of the V2GeC nanolaminate result fromthe chemical bonds with the anisotropic pattern as shown inthis work.

  • 27.
    Magnuson, Martin
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik.
    Mattesini, Maurizio
    University Complutense Madrid.
    Höglund, Carina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Abrikosov, Igor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Birch, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Electronic structure investigation of the cubic inverse perovskite Sc3AlN2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, nr 23, s. 235102-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure and chemical bonding of the recently discovered inverse perovskite Sc3AlN, in comparison to those of ScN and Sc metal, have been investigated by bulk-sensitive soft-x-ray emission spectroscopy. The measured Sc L, N K, Al L-1, and Al L-2,L-3 emission spectra are compared with calculated spectra using first-principles density-functional theory including dipole transition-matrix elements. The main Sc 3d-N 2p and Sc 3d-Al 3p chemical bond regions are identified at -4 and -1.4 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states in the Al L-2,L-3 emission from Sc3AlN in comparison to that for pure Al metal is found, which reflects the Sc 3d-Al 3p hybridization observed in the Al L-1 emission. The differences between the electronic structures of Sc3AlN, ScN, and Sc metal are discussed in relation to the change in the conductivity and elastic properties.

  • 28.
    Magnuson, Martin
    Linköpings universitet, Institutionen för fysik, kemi och biologi. Linköpings universitet, Tekniska högskolan.
    RIXS Investigation of Zhang-Rice Excitations in single-crystal YBa2Cu3O7-x2008Rapport (Övrigt vetenskapligt)
  • 29.
    Magnuson, Martin
    et al.
    Uppsala University.
    Mattesini, M.
    Departamento de Física de la Tierra, Astronomía y Astrofísica I, Universidad Complutense de Madrid.
    Li, S.
    Uppsala University.
    Höglund, Carina
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Eriksson, O.
    Uppsala University.
    Bonding mechanism in the nitrides Ti2AlN and TiN: An experimental and theoretical investigation2007Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, nr 195127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theelectronic structure of nanolaminate Ti2AlN and TiN thin films hasbeen investigated by bulk-sensitive soft x-ray emission spectroscopy. The measuredTi L2,3, N K, Al L1, and Al L2,3 emissionspectra are compared with calculated spectra using ab initio density-functionaltheory including dipole transition-matrix elements. Three different types of bondregions are identified; a relatively weak Ti  3d-Al  3p bonding between −1and −2  eV below the Fermi level, and Ti  3d-N  2p and Ti  3d-N  2sbondings which are deeper in energy observed at −4.8  eV and−15  eV below the Fermi level, respectively. A strongly modified spectralshape of 3s states of Al L2,3 emission from Ti2AlNin comparison with pure Al metal is found, which reflectsthe Ti  3d-Al  3p hybridization observed in the Al L1 emission. Thedifferences between the electronic and crystal structures of Ti2AlN andTiN are discussed in relation to the intercalated Al layersof the former compound and the change of the materialsproperties in comparison with the isostructural carbides.

  • 30.
    Magnuson, Martin
    Department of Physics, Uppsala University.
    Electronic structure investigation of MAX-phases by soft x-ray emission spectroscopy2007Ingår i: MRS Online Proceedings Library, Volume 1023 / [ed] E. Ivers-Tiffee and S. Barnett, 2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    The electronic structure of nanolaminate Ti2AlC and Ti2AlN thin films, so-called MAX-phases, were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitride compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. The Ti-Al bonding is manifested by a pronounced peak in the Ti L-emission of Ti2AlC and Ti2AlN that is not present in the binary TiC system. The spectral shape of Al L-emission in the MAX-phase is strongly modified in comparison to metallic Al. By replacing or partly exchanging C with N, a change of the electron population can be achieved causing a change of covalent bonding between the laminated layers, which enables control of the material properties.

  • 31.
    Magnuson, Martin
    Uppsala University.
    Investigation of Ti2AlC and TiC by soft x-ray emission spectroscopy2007Ingår i: Journal of Physics: Conference Series 61 / [ed] Ernst Meyer, Martin Hegner, Christoph Gerber and Hans-Joachim Güntherodt, 2007, s. 760-764Konferensbidrag (Refereegranskat)
    Abstract [en]

    The electronic structure of the MAX-phase Ti pectroscopy. This nanolaminated carbide compound represents a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft x-ray emission technique is shown to be particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. The Ti-Al bonding is manifested by a pronounced peak in the Ti present in the binary TiC system. The spectral shape of Al in comparison to metallic Al. By replacing the constituting elements, a change of the electron population can be achieved causing a change of covalent bonding between the laminated layers, which enables control of the macroscopic properties of the material. 

  • 32.
    Duda, L.-C.
    et al.
    Department of Physics,Uppsala University, Uppsala, Sweden.
    Schmitt, T.
    Department of Physics,Uppsala University, Uppsala, Sweden / Swiss Light Source, Paul Scherrer Institute, Switzerland.
    Magnuson, Martin
    Department of Physics,Uppsala University, Uppsala, Sweden.
    Forsberg, J.
    Department of Physics,Uppsala University, Uppsala, Sweden.
    Olsson, A.
    Department of Physics,Uppsala University, Uppsala, Sweden.
    Nordgren, J.
    Department of Physics,Uppsala University, Uppsala, Sweden.
    Okada, K.
    The Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
    Kotani, A.
    RIKEN/Spring8,1-1-1 Kouto, Mikazuki-cho, Saya-gun, Hyogo,Japanand / Photon Factory, IMSS, High Energy Accelerator Research Organization,Tsukuba, Ibaragi, Japan .
    Resonant inelastic X-ray scattering at the NiO O K-resonance: non-local charge-transfer and double singlet excitations2007Ingår i: MAX-lab: Activity Report 2005-2006 / [ed] U. Johansson, A. Nyberg, R. Nyholm, H. Ullman, Lund: MAX-lab , 2007, s. 270-271Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    NiO is one of the prototypical compounds that has highlighted the importance of correlation effects in transition metal oxides. Core level spectroscopies bear evidence for the highly correlated nature of low energy excitations. For instance, the asymmetry of the Ni2p-line shape has been attributed to non-local charge transfer excitations and multi-site cluster calculations show that solidstate effects generally are appreciable for correlated materials, such as cuprates and high Tc-compounds.....

  • 33.
    Magnuson, Martin
    et al.
    Uppsala University.
    Wilhelmsson, O.
    Uppsala University.
    Palmquist, J.-P.
    Uppsala University.
    Jansson, U.
    Uppsala University.
    Mattesini, M.
    Universidad Complutense de Madrid.
    Li, S.
    Uppsala University.
    Ahuja, R.
    Uppsala University.
    Eriksson, O.
    Uppsala University.
    Electronic structure and chemical bonding in Ti2AlC investigated by soft x-ray emission spectroscopy2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 195108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theelectronic structure of the nanolaminated transition metal carbide Ti2AlC hasbeen investigated by bulk-sensitive soft x-ray emission spectroscopy. The measuredTi L, C K, and Al L emission spectra arecompared with calculated spectra using ab initio density-functional theory includingdipole matrix elements. The detailed investigation of the electronic structureand chemical bonding provides increased understanding of the physical propertiesof this type of nanolaminates. Three different types of bondregions are identified: The relatively weak Ti 3d–Al 3p bond1  eV below the Fermi level and the Ti 3d–C 2pand Ti 3d–C 2s bonds which are stronger and deeperin energy are observed around 2.5 and 10  eV below theFermi level, respectively. A strongly modified spectral shape of the3s final states in comparison to pure Al is detectedfor the intercalated Al monolayers indirectly reflecting the Ti 3d–Al3p hybridization. The differences between the electronic and crystal structuresof Ti2AlC, Ti3AlC2, and TiC are discussed in relation tothe number of Al layers per Ti layer in thetwo former systems and the corresponding change of the unusualmaterials properties.

  • 34.
    Magnuson, Martin
    et al.
    Uppsala University.
    Mattesini, M.
    Uppala University.
    Wilhelmsson, Ola
    Uppsala University.
    Emmerlich, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Palmquist, Jens-Petter
    Uppsala University.
    Li, Sa
    Uppsala University.
    Ahuja, Rajeev
    Uppsala University.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Eriksson, Olle
    Uppsala University.
    Jansson, Ulf
    Uppsala University.
    Electronic structure and chemical bonding in Ti4SiC3 investigated by soft x-ray emission spectroscopy and first-principles theory2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theelectronic structure in the new transition-metal carbide Ti4SiC3 has beeninvestigated by bulk-sensitive soft x-ray emission spectroscopy and compared tothe well-studied Ti3SiC2 and TiC systems. The measured high-resolution TiL, C K, and Si L x-ray emission spectra arediscussed with ab initio calculations based on density-functional theory includingcore-to-valence dipole matrix elements. The detailed investigations of the Ti-Cand Ti-Si chemical bonds provide increased understanding of the physicalproperties of these nanolaminates. A strongly modified spectral shape isdetected for the intercalated Si monolayers due to Si 3phybridization with the Ti 3d orbitals. As a result ofrelaxation of the crystal structure and the charge-transfer from Ti(and Si) to C, the strength of the Ti-C covalentbond is increased. The differences between the electronic and crystalstructures of Ti4SiC3 and Ti3SiC2 are discussed in relation tothe number of Si layers per Ti layer in thetwo systems and the corresponding change of materials properties.

  • 35.
    Magnuson, Martin
    et al.
    Uppsala University.
    Duda, L.-C.
    Uppsala University.
    Butorin, S. M.
    Uppsala University.
    Kuiper, P.
    Växjö University.
    Nordgren, J.
    Uppsala University.
    Large magnetic circular dichroism in resonant inelastic x-ray scattering at the Mn L-edge of Mn-Zn ferrite2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 172409Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 36.
    Magnuson, Martin
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Fahlman, Mats
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Ytors Fysik och Kemi. Linköpings universitet, Tekniska högskolan.
    Uhrberg, Roger
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Yt- och Halvledarfysik.
    Johansson, Leif
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial.
    Total of 100 authors in alphabetical orders, -
    MAX IV Conceptual Design Report (CDR)2006Rapport (Övrigt vetenskapligt)
  • 37.
    Magnuson, Martin
    Department of Physics, Uppsala University.
    Max-Phases Investigated by Soft X-Ray Emission Spectroscopy2006Ingår i: Mechanical Properties and Performance of Engineering Ceramics II: Ceramic Engineering and Science Proceedings, Volume 7, Issue 2 / [ed] Rajan Tandon, Andrew Wereszczak, Edgar Lara-Curzio, 2006, s. 325-329Konferensbidrag (Refereegranskat)
    Abstract [en]

    The electronic structures of the MAX-phases Ti3AlC2, Ti3SiC2 and Ti3GeC2 were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is shown to be particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L-emission of Ti3AlC2. When Al is replaced by Si or Ge, the shoulder disappears. Furthermore, the spectral shapes of Al, Si and Ge in the MAX-phases are strongly modified in comparison to the corresponding pure elements. By varying the constituting elements, a change of the electron population is achieved causing a change of covalent bonding between the laminated layers, which enables control of the macroscopic properties of the material.

  • 38.
    Duda, L.-C.
    et al.
    Uppsala University.
    Schmitt, T.
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Forsberg, J.
    Uppsala University.
    Olsson, A.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Okada, K.
    Uppsala University.
    Kotani, A.
    Uppsala University.
    Reply to comment by Hüfner on "Resonant Inelastic X-Ray Scattering at the Oxygen K Resonance of NiO: Nonlocal Charge Transfer and Double-Singlet Excitations"2006Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, nr 269702Artikel i tidskrift (Övrigt vetenskapligt)
  • 39.
    Duda, L.-C.
    et al.
    Uppsala University.
    Schmitt, T.
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Forsberg, J.
    Uppsala University.
    Olsson, A.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Okada, K.
    Okayama University.
    Kotani, A.
    RIKEN/Spring8.
    Resonant Inelastic X-Ray Scattering at the Oxygen K Resonance of NiO: Nonlocal Charge Transfer and Double-Singlet Excitations2006Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, nr 067402Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report high-resolution polarization-dependent resonant inelastic x-ray scattering (RIXS) at the O K resonance of NiO showing a rich excitation spectrum. We perform multisite Ni6O19 cluster model calculations, revealing that solid state effects are substantial. We identify a nonlocal charge transfer excitation at 4–5 eV and double-singlet creation at 1.75 eV, both exhibiting significant scattering geometry dependence. Apart from an intense band of local charge transfer excitations (above 5 eV) also dd excitations at 1 eV are observed. Finally, we point out that O K RIXS of correlated metal oxides allows a quantitative and consistent determination of the charge transfer energy and the Hund coupling energy JH.

  • 40.
    Fink, Reinhold F.
    et al.
    Uppsala University.
    Eschner, Annika
    University of Lund.
    Magnuson, Martin
    Uppsala University.
    Björneholm, Olle
    Uppsala University.
    Hjelte, Ingela
    Uppsala University.
    Miron, Catalin
    University of Lund.
    Bässler, Margit
    University of Lund.
    Svensson, Svante
    Uppsala University.
    Novella Piancastelli, Maria
    Uppsala University.
    Sörensen, Stacey L.
    University of Lund.
    Specific production of very long-lived core-excited sulphur atoms by 2p-1s excitation of the OCS molecule followed by ultrafast dissociation2006Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, nr 12, s. L269-L275Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A core-excited sulfur state with a lifetime almost one order of magnitude longer than in molecular 2p core-hole states is selectively produced by ultrafast dissociation of S 2p → σ* excited OCS. Clear evidence for this is provided by strong atomic peaks (20% of the total intensity) in x-ray fluorescence but very weak ones (2%) in the corresponding resonant Auger spectrum. Corroborating the assignment of the spectra, ab initio calculations explain the enhanced lifetime: the Auger decay of the produced 3D3 (2p53p5) sulfur state is strongly decreased as it contradicts a newly derived propensity rule of the L2,3MM Auger decay.

  • 41.
    Magnuson, Martin
    et al.
    Uppsala University.
    Butorin, Sergei M.
    Uppsala University.
    Werme, Lars
    Uppsala University.
    Nordgren, Joseph
    Uppsala University.
    Ivanov, Kirill E.
    RRC Kurchatov Institute, Moscow.
    Guo, Jinghua
    Lawrence Berkeley National Laboratory, Berkeley, USA.
    Shuh, David K.
    Lawrence Berkeley National Laboratory, Berkeley, USA.
    Uranium oxides investigated by X-ray absorption and emission spectroscopies2006Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, nr 115, s. 5615-6518Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 42.
    Magnuson, Martin
    et al.
    Uppsala University.
    Palmquist, Jens-Petter
    Uppsala University.
    Mattesini, M.
    Uppsala University.
    Li, Sa
    Uppsala University.
    Ahuja, Rajeev
    Uppsala University.
    Eriksson, Olle
    Uppsala University.
    Emmerlich, Jens
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Wilhelmsson, Ola
    Uppsala University.
    Eklund, Per
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Högberg, Hans
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Hultman, Lars
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
    Jansson, Ulf
    Uppsala University.
    Electronic structure investigation of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 by soft x-ray emission spectroscopy2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structures of epitaxially grown films of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L , C K , Al L , Si L , and Ge M emission spectra are compared with ab initio density-functional theory including core-to-valence dipole matrix elements. A qualitative agreement between experiment and theory is obtained. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L emission of Ti3AlC2 . As Al is replaced with Si or Ge, the shoulder disappears. For the buried Al and Si layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and Ti3SiC2 , respectively. As a result of relaxation of the crystal structure and the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened. The differences between the electronic structures are discussed in relation to the bonding in the nanolaminates and the corresponding change of materials properties.

  • 43.
    Magnuson, Martin
    Uppsala University.
    Engagerad Fysiker Fyller Fyrtio År2005Rapport (Övrig (populärvetenskap, debatt, mm))
  • 44.
    Fink, Reinhold F.
    et al.
    Uppsala University.
    Eschner, Annika
    University of Lund.
    Magnuson, Martin
    Uppsala University.
    Björneholm, Olle
    Uppsala University.
    Hjelte, Ingela
    Uppsala University.
    Miron, Catalin
    University of Lund.
    Bässler, Margit
    University of Lund.
    Svensson, Svante
    Uppsala University.
    Piancastelli, Maria Novella
    Uppsala University.
    Sörensen, Stacey L.
    University of Lund.
    Long-lived highly excited sulphur atoms produced by ultrafast doissociation of 2p-1sigma*-excited OCS molecules2005Rapport (Övrigt vetenskapligt)
  • 45.
    Magnuson, Martin
    Uppsala University.
    Mjukröntgen i Nanovärlden2005Rapport (Övrig (populärvetenskap, debatt, mm))
  • 46.
    Yablonskikh M. V., M. V.
    et al.
    Uppsala University.
    Yarmoshenko, Yu. M.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Solovyev, I. V.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Kurmaev, E. Z.
    Russian Academy of Sciences-Ural Division, Yekaterinburg .
    Duda, L.-C.
    Uppsala University.
    Schmitt, Thorsten
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Nordgren, Joseph
    Uppsala University.
    Moewes, Alexander
    University of Saskatchewan, Saskatoon, Canada .
    Resonant L_alpha,betha X-ray emission and L2,3 X-ray absorption spectra of 3d metals in Co2MnZ (Z=Al,Ga,Sn,Sb) Heusler alloys as an element-selectve probe of spin character of valence band2005Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 144-147, s. 765-769Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The 3d metal resonant X-ray emission spectra (RXES) and L3,2 X-ray absorption spectra (XAS) of the Co2MnZ (Z=Al, Ga, Sn, Sb) alloys were measured using linearly polarized soft X-rays. The Mn and Co spectra are compared with results of spin-polarized calculations of Mn 3d and Co 3d partial densities of states performed for each alloy. It is found that a satellite observed at the high-energy side of Mn spectra is due to the localized Mn 3d states located above the Fermi energy. It is shown that the presence of the same satellite structure indicates a higher degree of spin-polarization of Mn 3d states than Co 3d states.

    Both the intensity of the satellite structure in Mn spectra and the /, peak ratio are increased and follow the atomic number of Z element. The effect is especially strong when excitating slightly above the L3 and L2 threshold energies as well as at resonance. We observe a correlation between these spectral parameters and the magnitude of local magnetic moment. The changes occurring in the Mn RXES are in good agreement with a predicted decrease in p–d hybridization (between the atoms of Z element and Mn atoms). The calculated local density of Mn 3d states at the Fermi energy follows the same trend as the hybridization. This suggests that RXES of 3d metals can be used to monitor the degree of spin-polarization of the valence band states and the local density of states at the Fermi level. Note that neither the Mn L2,3 absorption nor the Co L2,3 and Co emission spectra of the alloys are affected by the different composition (different Z elements).

  • 47.
    Magnuson, Martin
    et al.
    Université Pierre et Marie Curie, Paris.
    Hague, Coryn
    Université Pierre et Marie Curie, Paris.
    Determination of the refractive index at soft X-ray resonances2004Ingår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 137, s. 519-522Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dispersive part of the refractive index, 1−δ, of vanadium is determined by measuring the angular dependence of the Bragg peak at the V L2,3 edge energy region using a Fe/V superlattice. This X-ray scattering technique provides access to the direct determination of the dispersive part of the refractive index across an absorption resonance and to the change of values from below unity to above unity. We demonstrate that previously tabulated values tend to underestimate the amplitude of the change in the real part of the refractive index. We also examine the need for applying absorption and polarization corrections.

  • 48.
    Magnuson, Martin
    et al.
    Uppsala University.
    Butorin, S. M.
    Uppsala University.
    Såthe, C.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Ravindran, P.
    University of Oslo.
    Spin transition in LaCoO3 investigated by resonant soft X-ray emission spectroscopy2004Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 68, nr 2, s. 289-295Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The spin transition in LaCoO3 is investigated by temperature-dependent resonant soft X-ray emission spectroscopy near the Co 2p absorption edges. This element-specific technique is more bulk sensitive with respect to the temperature-induced spin state of the Co3+ ions in LaCoO3 than other high-energy spectroscopic methods. The spin transition is interpreted and discussed with ab initio density-functional theory within the fixed-spin moment method, which is found to yield consistent spectral functions to the experimental data. The spectral changes for LaCoO3 as a function of temperature suggest a change in spin state as the temperature is raised from 85 to 300 K, while the system remains in the same spin state as the temperature is further increased to 510 K.

  • 49.
    Magnuson, Martin
    et al.
    Uppsala University.
    Rubensson, J.-E.
    Uppsala University.
    Föhlisch, A.
    Uppsala University.
    Wassdahl, N.
    Uppsala University.
    Nilsson, A.
    Uppsala University.
    Mårtensson, N.
    Uppsala University.
    X-ray fluorescence spectra of metals excited below threshold2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 045119Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    X-ray scattering spectra of Cu and Ni metals have been measured using monochromatic synchrotron radiation tuned from far above to more than 10 eV below threshold. Energy conservation in the scattering process is found to be sufficient to explain the modulation of the spectral shape, neglecting momentum conservation and channel interference. At excitation energies close to and above threshold, the emission spectra map the occupied local partial density of states. For the subthreshold excitations, the high-energy flank of the inelastic scattering exhibits a Raman-type linear dispersion, and an asymmetric low-energy tail develops. For excitation far below threshold the emission spectra are proportional to a convolution of the occupied and unoccupied local partial densities of states.

  • 50.
    Magnuson, Martin
    et al.
    Uppsala University.
    Butorin, S. M.
    Uppsala University.
    Guo, J.-H.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Electronic structure investigation of CoO by means of soft x-ray scattering2002Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 65, nr 205106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure of CoO is studied by resonant inelastic soft x-ray scattering spectroscopy using photon energies across the Co 2p absorption edges. The different energy-loss structures in the Raman scattering spectra are identified as due to d-d and charge-transfer excitations. For excitation energies close to the L3 resonance, the spectral features are dominated by quartet-quartet and quartet-doublet transitions of the 3d7 configuration. At excitation energies corresponding to the satellites in the Co 2p x-ray-absorption spectrum of CoO, the emission features are instead dominated by charge-transfer transitions to the 3d8-1 final state. The spectra are interpreted and discussed with the support of simulations within the single-impurity Anderson model with full multiplet effects which are found to yield consistent spectral functions to the experimental data.

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