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Sökning: WAKA:ref > Eriksson Olle > Rusz Jan

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1.
  • Bhowmick, Somnath, et al. (författare)
  • X-ray absorption spectra : Graphene, h-BN, and their alloy
  • 2013
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 87:15, s. 155108
  • Tidskriftsartikel (refereegranskat)abstract
    • Using first-principles density functional theory calculations, in conjunction with the Mahan-Nozieres-de Dominicis theory, we calculate the x-ray absorption spectra of the alloys of graphene and monolayer hexagonal boron nitride on a Ni (111) substrate. The chemical neighborhood of the constituent atoms (B, C, and N) inside the alloy differs from that of the parent phases. In a systematic way, we capture the change in the K-edge spectral shape, depending on the chemical neighborhood of B, C, and N. Our work also reiterates the importance of the dynamical core-hole screening for a proper description of the x-ray absorption process in sp(2)-bonded layered materials.
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2.
  • Bidermane, Ieva, et al. (författare)
  • Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine
  • 2013
  • Ingår i: Journal of Chemical Physics. - American Institute of Physics (AIP). - 0021-9606. ; 138:23, s. 234701
  • Tidskriftsartikel (refereegranskat)abstract
    • Using Near Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy, the thickness dependent formation of Lutetium Phthalocyanine (LuPc2) films on a stepped passivated Si(100)2x1 reconstructed surface was studied. Density functional theory (DFT) calculations were employed to gain detailed insights into the electronic structure. Photoelectron spectroscopy measurements have not revealed any noticeable interaction of LuPc2 with the H-passivated Si surface. The presented study can be considered to give a comprehensive description of the LuPc2 molecular electronic structure. The DFT calculations reveal the interaction of the two molecular rings with each other and with the metallic center forming new kinds of orbitals in between the phthalocyanine rings, which allows to better understand the experimentally obtained NEXAFS results.
3.
  • Delczeg-Czirjak, Erna K., et al. (författare)
  • Stabilization of the tetragonal distortion of Fe chi Co1-chi alloys by C impurities : A potential new permanent magnet
  • 2014
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 89:14, s. 144403
  • Tidskriftsartikel (refereegranskat)abstract
    • We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, which in turn leads to an enhanced magnetocrystalline anisotropy energy of up to 0.75 MJ/m(3) and a saturated magnetization field of 1.9 T.
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4.
  • Kocevski, Vancho, et al. (författare)
  • Transition between direct and indirect band gap in silicon nanocrystals
  • 2013
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 87:24, s. 245401
  • Tidskriftsartikel (refereegranskat)abstract
    • Using ground-state density functional theory we study the transition from indirect to direct band gap in hydrogen-terminated silicon nanocrystals (NCs) as a function of decreasing diameter. The studied range, from 1.0 to 4.6 nm diameter of nanocrystals, with spherical and Wulff-shape NCs, covers the transition from nano-to bulk regime. A change in the symmetry of the lowest unoccupied state as a function of decreasing NC diameter is observed, gradually increasing the oscillator strength of transitions from the highest occupied to the lowest unoccupied state. Real space and Fourier space characteristics of highest occupied and lowest unoccupied states are explored in detail and linked to a smooth transition from nano-to bulk regime.
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10.
  • Lidbaum, H, et al. (författare)
  • EMCD in the TEM - Optimization of signal acquisition and data evaluation
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • The method of electron magnetic circular dichroism (EMCD) was recently proposed anddemonstrated by Peter Schattschneider et al. [I]. The EMCD signal consists in differences of L3 andL2 edge intensities of ferromagnetic materials at specific diffraction vectors. EMCD is thereforeelement specific. Furthermore. it was shown recently that sum rules apply to the EMCD methodwhich is an essential progress to obtain quantitative magnetic information from this method [2-3].Though. the theoretical derivations of sum rule suppose that the obtained spin- to orbital magneticmoments do not depend on the choice of scattering vector. This is a simplification which must beverified both by simulations and experiments to make EMCD a quantitative method for the study ofmagnetic moments.In the experiment. the dichroic signal. i.e. the change ofLJ and L2 edges at different diffractionvectors is small. i.e. of the order of 5-15% of the total signal intensity. Therefore. the acquisitionconditions must be optimized to both approach a di ffraction geometry where sum rules can beapplied and to maximize the signal to noise ratio.In this work. we optimize both. the signal and the signal/noise ratio. The experiments were carriedout on a FEI Tecnai F30 equipped with a Gatan GIF2002 energy filter. Instead of recording k-vectordependent single spectra as in the original work [I], we acquire energy filtered diffraction patternsin the energy interval around the transition metal L-edge. This allows for extraction of the EMCDsignal at k-vectors where the signal contains quantitative magnetic information. All measurementsof2 dimensional k-space maps of the EMCD signal are compared with simulations of the EM CDsignal. We find very good agreement between theoretical predictions and experimental values forboth. the k-space evolution and quantitative agreement the EMCD signal. The data evaluationincludes a careful normalization procedure. a statistical optimization of the signal to noise ratio aswell as the consideration of the entire edge intensity. Finally. we demonstrate the quantitativeprecision of the proposed method at the example ofa slightly textured iron layer (figures I and 2).References[I] P Schattschneider et aJ.. Nature 44 I (2006) 486.[2] J. Rusz, O. Eriksson, P. Novak, P. M. Oppeneer. Phys. Rev. B 76 (2007) 060408.[3] L. Calmels et aJ.. Phys. Rev. B 76 (2007) 060409.
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  • Resultat 1-10 av 23
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