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  • Resultat 1-10 av 426
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  • Grigoriev, Anton, et al. (författare)
  • Electron transport in stretched monoatomic gold wires
  • 2006
  • Ingår i: Physical Review Letters. - 0031-9007. ; 97:23, s. 236807
  • Tidskriftsartikel (refereegranskat)abstract
    • The conductance of monoatomic gold wires containing 3-7 gold atoms has been obtained from ab initio calculations. The transmission is found to vary significantly depending on the wire stretching and the number of incorporated atoms. Such oscillations are determined by the electronic structure of the one-dimensional (1D) part of the wire between the contacts. Our results indicate that the conductivity of 1D wires can be suppressed without breaking the contact.
  • Laukkanen, P., et al. (författare)
  • Bismuth-stabilized c(2X6) reconstruction on a InSb(100) substrate Violation of the electron counting model
  • 2010
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 81:3
  • Tidskriftsartikel (refereegranskat)abstract
    • By means of scanning tunneling microscopy/spectroscopy (STM/STS), photoelectron spectroscopy, and first-principles calculations, we have studied the bismuth (Bi) adsorbate-stabilized InSb(100) substrate surface which shows a c(2X6) low-energy electron diffraction pattern [thus labeled Bi/InSb(100)c(2X6) surface] and which includes areas with metallic STS curves as well as areas with semiconducting STS curves. The first-principles phase diagram of the Bi/InSb(100) surface demonstrates the presence of the Bi-stabilized metallic c(2X6) reconstruction and semiconducting (4X3) reconstruction depending on the chemical potentials, in good agreement with STS results. The existence of the metallic c(2X6) phase, which does not obey the electron counting model, is attributed to the partial prohibition of the relaxation in the direction perpendicular to dimer rows in the competing reconstructions and the peculiar stability of the Bi-stabilized dimer rows. Based on (i) first-principles phase diagram, (ii) STS results, and (iii) comparison of the measured and calculated STM and photoemission data, we show that the measured Bi/InSb(100)c(2X6) surface includes metallic areas with the stable c(2X6) atomic structure and semiconducting areas with the stable (4X3) atomic structure.
  • Punkkinen, M. P. J., et al. (författare)
  • Bismuth-stabilized (2x1) and (2x4) reconstructions on GaAs(100) surfaces : Combined first-principles, photoemission, and scanning tunneling microscopy study
  • 2008
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 78:19
  • Tidskriftsartikel (refereegranskat)abstract
    • Bismuth adsorbate-stabilized (2x1) and (2x4) reconstructions of the GaAs(100) surfaces have been studied by first-principles calculations, valence-band and core-level photoelectron spectroscopies, and scanning tunneling microscopy. It is demonstrated that large Bi atom size leads to the formation of the pseudogap at the Fermi energy and to the lower energy of an adsorbate-derived surface band, which contributes to the stabilization of the exceptional Bi/GaAs(100)(2x1) reconstruction. It is proposed that the Bi/GaAs(100)(2x4) reconstructions include asymmetric mixed Bi-As dimers, in addition to the Bi-Bi dimers. Based on the calculations, we solve the atomic origins of the surface core-level shifts (SCLSs) of the Bi 5d photoemission spectra from the Bi/GaAs(100)(2x4) surfaces. This allows for resolving the puzzle related to the identification of two SCLS components often found in the measurements of the Bi 5d and Sb 4d core-level emissions of the Bi/III-V and Sb/III-V(100)(2x4) surfaces. Finally, the reason for the absence of the common (2x4)-beta 2 structure and additional support for the stability of the (2x1) structure on the Bi/III-V(100) surfaces are discussed in terms of Bi atom size and subsurface stress.
  • Laukkanen, P., 0, et al. (författare)
  • Anomalous bismuth-stabilized (2x1) reconstructions on GaAs(100) and InP(100) surfaces
  • 2008
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007 .- 1079-7114. ; 100:8, s. 086101
  • Tidskriftsartikel (refereegranskat)abstract
    • First-principles phase diagrams of bismuth-stabilized GaAs- and InP(100) surfaces demonstrate for the first time the presence of anomalous (2 x 1) reconstructions, which disobey the common electron counting principle. Combining these theoretical results with our scanning-tunneling-microscopy and photoemission measurements, we identify novel (2 x 1) surface structures, which are composed of symmetric Bi-Bi and asymmetric mixed Bi-As and Bi-P dimers, and find that they are stabilized by stress relief and pseudogap formation.
  • Belonoshko, Anatoly B., et al. (författare)
  • Quasi ab initio molecular dynamic study of Cu melting
  • 2000
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 61:6, s. 3838-3844
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the melting of Cu theoretically by means of a molecular dynamic method employing the Sutton-Chen model for the interatomic interaction. This interaction has been fitted to reproduce results from first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital method for the bcc, fee, hcp, and liquid configurations. No experimental data were used to tune the potential. A large number of properties including equation of state, melting temperature, high-pressure melting curve, change of volume and entropy at melting, liquid structure, diffusion coefficient in liquid, and vacancy formation energy are all in good agreement with experimental data. Inclusion of the full potential energy of a liquid configuration in the fitting procedure is critical for obtaining good agreement with experiment. Different ways to calculate the melting transition are shown to produce very different results. The use of a large number of particles in combination with the solid-liquid interface as an initial configuration in the simulation is essential in order to obtain the correct melting temperatures.
  • Isaev EI, Lichtenstein AI, Vekilov YK, Smirnova EA, Abrikosov IA, Simak SI, Ahuja R, Johansson B, et al. (författare)
  • Ab initio phonon calculations for Ll(2) Ni3Al and B2NiAl
  • 2004
  • Ingår i: Solid State Communications. - 0038-1098. ; 129:12, s. 809-814
  • Tidskriftsartikel (refereegranskat)abstract
    • The phonon spectra and phonon density of states of the Ni3Al and NiAl intermetallic compounds are calculated from first principles using the linear response method in conjunction with ultrasoft pseudopotentials. The calculated phonon dispersion curves are in good agreement with available experimental results from inelastic neutron scattering.
  • Skorodumova, N. V., et al. (författare)
  • Electronic, bonding, and optical properties of CeO2 and Ce2O3 from first principles
  • 2001
  • Ingår i: PHYSICAL REVIEW B. ; 64
  • Tidskriftsartikel (refereegranskat)abstract
    • First-principles electronic structure calculations of cerium oxide in two forms, CeO2 and Ce2O3, are Presented. The 4f state of Ce is treated as a part of the inner core in Ce2O3 and as a valence-band-like state in CeO2,. The calculated ground-state and magnetic properties of the Ce (III) oxide are shown to be in agreement with available experimental data as well as the calculated ground-state and optical properties of Ce (IV) dioxide. The nature of the bonding in cerium oxide is discussed on the basis of an analysis of the charge-density and electron localization function distributions and described as a polarized ionic bond in both oxides.
  • Ahuja, Rajeev, et al. (författare)
  • Optical properties of 4H-SiC
  • 2002
  • Ingår i: Journal of Applied Physics. - 0021-8979. ; 91:3, s. 2099-2103
  • Tidskriftsartikel (refereegranskat)abstract
    • The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies. © 2002 American Institute of Physics.
  • Andersson, D. A., et al. (författare)
  • Redox properties of CeO2-MO2 MO2 (M=Ti, Zr, Hf or Th) solid solutions from first principles calculations
  • 2007
  • Ingår i: Applied Physics Letters. - 0003-6951. ; 90:3, s. 031909
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors have used density functional theory calculations to investigate how the redox thermodynamics and kinetics of CeO2 are influenced by forming solid solutions with TiO2, ZrO2, HfO2, and ThO2. Reduction is facilitated by dissolving TiO2 (largest improvement), HfO2, or ZrO2 (least improvement), while ThO2 makes reduction slightly more difficult. The migration barrier is much lower in the neighborhood of a Ti (largest decrease), Hf, or Zr (least decrease), while the binding energy of solute ions and vacancies increases in the same sequence. They rationalize the properties of ceria solid solutions in terms of defect cluster relaxations.
  • Belonoshko, A. B., et al. (författare)
  • Xenon melting: : Density functional theory versus diamond anvil cell experiments
  • 2006
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829. ; 74, s. 054114
  • Tidskriftsartikel (refereegranskat)abstract
    • We performed two-phase ab initio density functional theory based molecular dynamics simulations of Xe melting and demonstrated that, contrary to claims in the recent literature, the pressure dependence of the Xe melting curve is consistent with the corresponding-states theory as well as with the melting curve obtained earlier from classical molecular dynamics with a Xe pair potential. While at low pressure the calculated melting curve is in perfect agreement with reliable experiments, our calculated melting temperatures at higher pressures are inconsistent with those from the most recent diamond anvil cell experiment. We discuss a possible explanation for this inconsistency.
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