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  • 1.
    Fallqvist, Amie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, National Supercomputer Centre (NSC). Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Belov, M. P.
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Resolving the debated atomic structure of the metastable cubic SiNx tissue phase in nanocomposites with TiN2018In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 9, article id 093608Article in journal (Refereed)
    Abstract [en]

    The TiN/SiNx nanocomposite and nanolaminate systems are the archetype for super if not ultrahard materials. Yet, the nature of the SiNx tissue phase is debated. Here, we show by atomically resolved electron microscopy methods that SiNx is epitaxially stabilized in a NaCl structure on the adjacent TiN(001) surfaces. Additionally, electron energy loss spectroscopy, supported by first-principles density functional theory calculations infer that SiNx hosts Si vacancies.

  • 2.
    Fallqvist, Amie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Evidence for B1-cubic SiNx by Aberration-Corrected Analytical STEMManuscript (preprint) (Other academic)
    Abstract [en]

    The crystal structure of epitaxially stabilized SiNx layers on TiN(001) was investigated by analytical aberration corrected electron microscopy. Atomically resolved images of the structure, which were acquired by scanning transmission electron microscopy using high angle annular dark field and annular bright field detectors, are used to identify the B1-cubic structure of SiNx. To corroborate the acquired images, image simulations were performed using candidate structures. Complementary to imaging, spatially resolved electron energy loss spectroscopy of the epitaxial SiNx layers was performed to acquire the symmetry specific nitrogen near edge fine-structure. Finally, full potential calculations performed to determine the near edge structure from candidate crystal structures confirms the existence of B1-cubic SiNx.

  • 3.
    Monteseguro, V
    et al.
    Univ Valencia, Spain; European Radiat Synchrotron Facil, France.
    Sans, J. A.
    Univ Politecn Valencia, Spain.
    Cuartero, V
    European Radiat Synchrotron Facil, France; Ctr Univ Def Zaragoza, Spain.
    Cova, F.
    European Radiat Synchrotron Facil, France.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Olovsson, Weine
    Linköping University, National Supercomputer Centre (NSC). Linköping University, Faculty of Science & Engineering.
    Popescu, C.
    ALBA CELLS, Spain.
    Pascarelli, S.
    European Radiat Synchrotron Facil, France.
    Garbarino, G.
    European Radiat Synchrotron Facil, France.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Irifune, T.
    Ehime Univ, Japan; Tokyo Inst Technol, Japan.
    Errandonea, D.
    Univ Valencia, Spain.
    Phase stability and electronic structure of iridium metal at the megabar range2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8940Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Olovsson, Weine
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Holmstroem, Erik
    University Austral Chile.
    Marten, Tobias
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Niklasson, Anders M N
    Los Alamos National Laboratory.
    Interface core-level shifts as a probe of embedded thin-film quality2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 8, p. 085431-Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Olovsson, Weine
    et al.
    Linköping University, National Supercomputer Centre (NSC). Linköping University, Faculty of Science & Engineering.
    Mizoguchi, Teruyasu
    Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Kontur, Stefan
    Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Zum Großen Windkanal 6, 12489 Berlin, Germany.
    Hellman, Olle
    Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, United States / Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, California 91125, United States.
    Tanaka, Isao
    Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan.
    Draxl, Claudia
    Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Zum Großen Windkanal 6, 12489 Berlin, Germany / European Theoretical Spectroscopy Facility (ETSF.
    Vibrational Effects in X-ray Absorption Spectra of Two-Dimensional Layered Materials2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 15, p. 9688-9692Article in journal (Refereed)
    Abstract [en]

    With the examples of the C K-edge in graphite and the B K-edge in hexagonal boron nitride, we demonstrate the impact of vibrational coupling and lattice distortions on the X-ray absorption near-edge structure (XANES) in two-dimensional layered materials. Theoretical XANES spectra are obtained by solving the Bethe–Salpeter equation of many-body perturbation theory, including excitonic effects through the correlated motion of the core hole and excited electron. We show that accounting for zero-point motion is important for the interpretation and understanding of the measured X-ray absorption fine structure in both materials, in particular for describing the σ*-peak structure.

  • 6.
    Olovsson, Weine
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Weinhardt, L
    University of Wurzburg, Germany.
    Fuchs, O
    University of Wurzburg, Germany.
    Tanaka, I
    Kyoto University, Japan.
    Puschnig, P
    University of Leoben, Austria.
    Umbach, E
    University of Wurzburg, Germany.
    Heske, C
    University of Wurzburg, Germany.
    Draxl, C
    University of Leoben, Austria.
    The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 31Article in journal (Refereed)
    Abstract [en]

    We have carried out a theoretical and experimental investigation of the beryllium K-edge soft x-ray absorption fine structure of beryllium compounds in the oxygen group, considering BeO, BeS, BeSe, and BeTe. Theoretical spectra are obtained ab initio, through many-body perturbation theory, by solving the Bethe–Salpeter equation (BSE), and by supercell calculations using the core-hole approximation. All calculations are performed with the full-potential linearized augmented plane-wave method. It is found that the two different theoretical approaches produce a similar fine structure, in good agreement with the experimental data. Using the BSE results, we interpret the spectra, distinguishing between bound core-excitons and higher energy excitations.

  • 7.
    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
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Magnuson, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    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 nitride2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 316, p. 232-236Article in journal (Refereed)
    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.

  • 8.
    Wang, Weimin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, Faculty of Science & Engineering.
    Band structure of hydrogenated silicene on Ag(111): Evidence for half-silicane2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 8, p. 081406-Article in journal (Refereed)
    Abstract [en]

    In the case of graphene, hydrogenation removes the conductivity due to the bands forming the Dirac cone by opening up a band gap. This type of chemical functionalization is of the utmost importance for electronic applications. As predicted by theoretical studies, a similar change in the band structure is expected for silicene, the closest analog to graphene. We here report a study of the atomic and electronic structures of hydrogenated silicene with hydrogen on one side, the so-called half-silicane. The ("2 root 3 x 2 root 3") phase of silicene on Ag(111) was used in this Rapid Communication since it can be formed homogeneously across the entire surface of the Ag substrate. Low-energy electron diffraction and scanning tunneling microscopy data clearly show that hydrogenation changes the structure of silicene on Ag(111) resulting in a (1 x 1) periodicity with respect to the silicene lattice. The hydrogenated silicene also exhibits a quasiregular ("2 root 3 x 2 root 3")-like arrangement of vacancies. Angle-resolved photoelectron spectroscopy revealed two dispersive bands which can be unambiguously assigned to half-silicane. The common top of these bands is located at similar to 0.9 eV below the Fermi level. We find that the experimental bands are closely reproduced by the theoretical band structure of free-standing silicene with H adsorbed on the upper hexagonal sublattice.

  • 9.
    Wang, Weimin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Uhrberg, Roger
    Linköping University, Department of Physics, Chemistry and Biology, Surface and Semiconductor Physics. Linköping University, Faculty of Science & Engineering.
    Experimental and theoretical determination of sigma bands on ("2 root 3 x 2 root 3") silicene grown on Ag(111)2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 20, p. 205427-Article in journal (Refereed)
    Abstract [en]

    Silicene, the two-dimensional (2D) allotrope of silicon, has very recently attracted a lot of attention. It has a structure that is similar to graphene and it is theoretically predicted to show the same kind of electronic properties which have put graphene into the focus of large research and development projects worldwide. In particular, a 2D structure made from Si is of high interest because of the application potential in Si-based electronic devices. However, so far there is not much known about the silicene band structure from experimental studies. A comprehensive study is here presented of the atomic and electronic structure of the silicene phase on Ag(111) denoted as (2 root 3 x 2 root 3)R30 degrees in the literature. Low energy electron diffraction (LEED) shows an unconventional rotated ("2 root 3 x 2 root 3") pattern with a complicated set of split diffraction spots. Scanning tunneling microscopy (STM) results reveal a Ag(111) surface that is homogeneously covered by the ("2 root 3 x 2 root 3") silicene which exhibits an additional quasiperiodic long-range ordered superstructure. The complex structure, revealed by STM, has been investigated in detail and we present a consistent picture of the silicene structure based on both STM and LEED. The homogeneous coverage by the ("2 root 3 x 2 root 3") silicene facilitated an angle-resolved photoelectron spectroscopy study which reveals a silicene band structure of unprecedented detail. Here we report four silicene bands which are compared to calculated dispersions based on a relaxed (2 root 3 x 2 root 3) model. We find good qualitative agreement between the experimentally observed bands and calculated silicene bands of sigma character.

  • 10.
    Xia, Chao
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Tal, Alexey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Johansson, Leif
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Linköping University, National Supercomputer Centre (NSC).
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Virojanadara, Chariya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Effects of rhenium on graphene grown on SiC(0001)2018In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 222, p. 117-121Article in journal (Refereed)
    Abstract [en]

    We study the effects of Rhenium (Re) deposited on epitaxial monolayer graphene grown on SiC(0001) and after subsequent annealing at different temperatures, by performing high resolution photoelectron spectroscopy (PES) and angle resolved photoelectron spectroscopy (ARPES). The graphene-Re system is found to be thermally stable. While no intercalation or chemical reaction of the Re is detected after deposition and subsequent annealing up to 1200 degrees C, a gradual decrease in the binding energy of the Re 4f doublet is observed. We propose that a larger mobility of the Re atoms with increasing annealing temperature and hopping of Re atoms between different defective sites on the graphene sample could induce this decrease of Re 4f binding energy. This is corroborated by first principles density functional theory (DFT) calculations of the Re core-level binding energy shift. No change in the doping or splitting of the initial monolayer graphene electronic band structure is observed after Re deposition and annealing up to 1200 degrees C, only a broadening of the bands. (C) 2017 Elsevier B.V. All rights reserved.

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