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  • 201. Hennies, F
    et al.
    Bao, Z
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Travnikova, O
    Piancastelli, M. N
    The Bonding of Chemisorbed Ethylene Oxide on Si (100) SurfaceManuscript (Other academic)
  • 202. Hergenhahn, Uwe
    et al.
    Barth, Silko
    Ulrich, Volker
    Mucke, Melanie
    Joshi, Sanjeev
    Lischke, Toralf
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Rander, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Öhrwall, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    3p valence photoelectron spectrum of Ar clusters2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 15, p. 155448-Article in journal (Refereed)
    Abstract [en]

    The shape of the outer valence (3p) photoelectron spectrum of Ar clusters is investigated by vacuum ultraviolet photoionization with synchrotron radiation. We show the dependence of the spectrum on cluster size and the change in its shape with photon energy. Inelastic losses due to intracluster photoelectron scattering are most important for changes in the photoelectron main line and explain the appearance of additional peaks. A comparison of our results to earlier work on bulk condensed Ar and Ar thin films is given. Evidence for a deviation of the photoionization cross sections for clusters from the atomic ones has not been found.

  • 203. Hikosaka, Y.
    et al.
    Lablanquie, P.
    Penent, F.
    Kaneyasu, T.
    Shigemasa, E.
    Feifel, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Soft X-Ray Physics.
    Eland, J. H. D.
    Ito, K.
    Energy Correlation of the Three Electrons Emitted during the Triple Photoionization of Ar2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 1, p. 013002-Article in journal (Refereed)
    Abstract [en]

    We report on an experimental investigation of energy correlation among three electrons emitted in valence triple photoionization (TPI) of Ar. The energy correlations reveal a predominant contribution from sequential TPI processes involving intermediate Ar2+ formation, which suggests that such indirect contributions should be included in the formulation of the threshold law for TPI cross sections. The differential cross section for direct TPI at about 150 eV above threshold producing one slow electron with a few eV kinetic energy is found to have a deeply hollow U-shaped profile in energy sharing between the other two electrons.

  • 204. Hild, K.
    et al.
    Maul, J.
    Schoenhense, G.
    Elmers, H. J.
    Amft, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Magnetic Circular Dichroism in Two-Photon Photoemission2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 5, p. 057207-Article in journal (Refereed)
    Abstract [en]

    We report the observation of magnetic circular dichroism (MCD) in two-photon photoemission (2PPE). The Heusler alloys Ni2MnGa and Co2FeSi were investigated by excitation with femtosecond laser light, showing MCD asymmetries of A = (3.5 +/- 0.5) x 10(-3) for Ni2MnGa and of A = (2.1 +/- 1.0) x 10(-3) for Co2FeSi, respectively. A theoretical explanation is provided based on local spin-density calculations for the magnetic dichroic response; the computed 2PPE MCD agrees well with the experiment. The observed 2PPE magnetic contrast represents an interesting alternative for future time-resolved photoemission studies on surface magnetism practicable in the laboratory.

  • 205.
    Hjörvarsson, Björgvin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Andersson, Gabriella
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Dura, J. A.
    Udovic, P.
    Isberg, P.
    Majkrzak, C. F.
    Temperature dependence of the magnetic interlayer ordering in Fe(3)/V(14)Hx (001) superlattices2008In: Superlattices and Microstructures, ISSN 0749-6036, E-ISSN 1096-3677, Vol. 43, no 2, p. 101-111Article in journal (Refereed)
    Abstract [en]

    The magnetic interlayer ordering in Fe(3)/V (14)Hx (001) superlattices exhibits dramatic changes on changing the hydrogen concentration. From initial antiferromagnetic (AF) coupling with , the introduction of H (H/V atomic ratio of 0.06) gives rise to ferromagnetic (FM) alignment at room temperature. When cooled, the magnetic ordering exhibits a transition from FM to a canted state below 200 K. Further increase of the hydrogen content (H/V ≈1) gives rise to FM-ordering at temperatures between 30 and 300 K.

  • 206. Hjörvarsson, Björgvin
    et al.
    Marcellini, Moreno
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Ahlberg, Martina
    Wolff, Maximilian
    The effect of boundaries on ordering in finite magnetsIn: Physical Review LettersArticle in journal (Refereed)
  • 207.
    Hjörvarsson, Björgvin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Pentcheva, R.
    Modern growth problems and growth techniques2008In: Magnetic Heterostructures, Advances and Perspectives in Spinstructures and Spintransport, Berlin: Springer , 2008, p. 1-44Chapter in book (Other academic)
  • 208.
    Hjörvarsson, Björgvin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Pentcheva, Rossitza
    Modern growth problems and growth techniques2008In: Springer Tracts in Modern Physics, ISSN 0081-3869, E-ISSN 1615-0430, Vol. 227, p. 1-44Article, review/survey (Refereed)
    Abstract [en]

    The growth and characterization of magnetic materials has progressed substantially during the last decades. In this chapter we give a brief overview of this vastly growing field of research. We highlight some of the relevant growth techniques for different materials classes but we do not intend to be complete with respect to technical details or materials systems. We also outline some of the concepts and theories of the growth of modern magnetic materials, emphasizing the role of first principles calculations in providing microscopic understanding of the growth mechanisms. We discuss the growth of metallic and oxide single crystal films, multilayers and superlattices and the influence of thickness, strain, crystallinity, structure and morphology on the resulting magnetic properties.

  • 209. Hu, Qing-Miao
    et al.
    Li, Shu-Jun
    Hao, Yu-Lin
    Yang, Rui
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Phase stability and elastic modulus of Ti alloys containing Nb, Zr, and/or Sn from first-principles calculations2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 12, p. 121902-Article in journal (Refereed)
    Abstract [en]

    The alloying effects of Nb, Zr, and/or Sn on the phase stability and elastic properties of Ti are investigated by using a first-principles method. Our calculation results indicate that a carefully designed Ti-Nb-Zr-Sn system can be a good candidate for low modulus biomedical materials. We find that the well-known correlation between the e/a ratio and both elastic and phase stabilities for Ti alloyed with transition metal elements breaks down for the Ti-Sn alloy.

  • 210.
    Huang, L. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Silvearv, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Araújo, C. Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Defect-induced strong ferromagnetism in Cr-doped In2O3 from first-principles theory2010In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 150, no 13-14, p. 663-665Article in journal (Refereed)
    Abstract [en]

    We demonstrate by means of first-principles calculations that the high Curie temperature observed in Cr-doped In2O3 is mediated by intrinsic p-type defects, namely In vacancies or O interstitials. Charge transfer from Cr 3d states to the hole states formed by these defects makes Cr ions in the mixed valence state, giving rise to a strong ferromagnetic coupling. Calculated formation energies of various defects also show that doping Cr in In2O3 could greatly lower the formation energies of p-type intrinsic defects even in oxygen-deficient growth conditions. These results advance our understanding of the underlying physics of diluted magnetic oxides. (C) 2009 Elsevier Ltd. All rights reserved.

  • 211.
    Häggström, Lennart
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Kamali, Saeed
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ahniyaz, Anwar
    Bergström, L.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Mössbauer and magnetisation studies of iron oxide  nanocrystals2008In: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 183, no 1-3, p. 49-53Article in journal (Refereed)
    Abstract [en]

    Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.

  • 212. Ingerman, Åke
    et al.
    Linder, Cedric
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Physics Didactics.
    Marshall, Delia
    The learners’ experience of variation: Following students’ threads of learning physics in computer simulation sessions2009In: Instructional science, ISSN 0020-4277, E-ISSN 1573-1952, Vol. 37, no 3, p. 273-292Article in journal (Refereed)
    Abstract [en]

    This article attempts to describe students' process of learning physics using the notion of experiencing variation as the basic mechanism for learning, and thus explores what variation, with respect to a particular object of learning, that students experience in their process of constituting understanding. Theoretically, the analysis relies on analytic tools from the phenomenographic research tradition, and the recent group of studies colloquially known as the variation theory of learning, having the notion of experiencing variation as a key for learning at its core. Empirically, the study relies on video and audio recordings of seven pairs of students interacting in a computer-simulation learning environment featuring Bohr's model of the atom. The data was analysed on a micro-level for the emergence of student-recognised variation, depicted in terms of 'threads of learning'. This was done by linking variation around aspects of the object of learning present in the situation, and attended to by the students, to new ways of seeing-characterised as an expanding anatomy of awareness, and hence as learning. The students' threads of learning are characterised in terms of two stages of learning progress: (1) discerning variation, and (2) constituting meaning from this experience of variation (experienced as holistically relevant in the students' conceptual domain of physics and the Bohr model). Two groups of threads of learning were identified: one where the variation experienced by students was within an aspect of the object of learning, and one where variation was across several aspects.

  • 213. Isvoranu, Cristina
    et al.
    Åhlund, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Ataman, Evren
    Mårtensson, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Andersen, Jesper N.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Schnadt, Joachim
    Electron spectroscopy study of the initial stages of iron phthalocyanine growth on highly oriented pyrolitic graphite2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, no 21, p. 214709-Article in journal (Refereed)
    Abstract [en]

    The nature of the intermolecular and substrate bonds of iron   phthalocyanine adsorbed on highly oriented pyrolitic graphite has been   investigated by x-ray photoelectron spectroscopy and x-ray absorption   spectroscopy. We find that the molecules grow in a highly ordered   fashion with the molecules essentially plane-parallel to the surface in   both the mono- and multilayers. The spectra obtained on both types of   film are virtually identical, which shows that the bonds both between   the adsorbate and substrate and between the molecular layers have a   pure van der Waals nature. Supporting density functional theory results   indicate that the layers are stabilized by weak hydrogen bonds within   the molecular layers.

  • 214.
    Iusan, Diana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Kabir, Mukul
    Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Microscopic picture of Co clustering in ZnO2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 12, p. 125202-Article in journal (Refereed)
    Abstract [en]

    Density functional theory was applied to study the chemical and magnetic interactions between Co atoms doped in ZnO. It was found that the Co impurities tend to form nanoclusters and the interactions between these atoms are antiferromagnetic within the local spin-density approximation (LSDA)+Hubbard U approach. The extracted interatomic exchange parameters agree reasonably well with recent experimental results. We have analyzed and compared the electronic structure obtained using the LSDA and LSDA+U approaches and found that the LSDA+U gives the most reasonable result, highlighting the importance of short-ranged antiferromagnetic interactions due to superexchange.

  • 215.
    Iusan, Diana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Coleman, Victoria A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Westin, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Wikberg, J. Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electronic structure and chemical and magnetic interactions in ZnO doped with Co and Al: Experiments and ab initio density-functional calculations2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 8, p. 085319-Article in journal (Refereed)
    Abstract [en]

    We present results of electronic structure and magnetization measurements of Co:ZnO and Co:ZnO codoped with Al thin-film samples fabricated by solution-based methods together with ab initio electronic structure calculations. Electronic structure measurements indicate that the Co states lie close to the valence-band edge with pinning of the Fermi level primarily due to native defects yielding a heavily n-doped material. The findings in the electronic structure measurements are corroborated by results from theoretical calculations. We find that it is necessary to go beyond the local-density approximation to achieve agreement with experiments. Moreover, the theoretical calculations indicate a tendency for the formation of Co clusters, giving rise to an antiferromagnetic exchange interaction between the Co atoms. The magnetization measurements are well in line with the theoretical predictions, showing a dominating superparamagnetic behavior arising from small antiferromagnetic clusters containing uncompensated spins.

  • 216.
    Iusan, Diana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Knut, Ronny
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Coleman, Victoria A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Westin, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Wikberg, J. Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electronic structure and chemical and magnetic interactions in ZnO doped with Co and Al: Experiments and ab initio density-functional calculations2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 8, p. 085319-Article in journal (Refereed)
    Abstract [en]

    We present results of electronic structure and magnetization measurements of Co:ZnO and Co:ZnO codoped with Al thin-film samples fabricated by solution-based methods together with ab initio electronic structure calculations. Electronic structure measurements indicate that the Co states lie close to the valence-band edge with pinning of the Fermi level primarily due to native defects yielding a heavily n-doped material. The findings in the electronic structure measurements are corroborated by results from theoretical calculations. We find that it is necessary to go beyond the local-density approximation to achieve agreement with experiments. Moreover, the theoretical calculations indicate a tendency for the formation of Co clusters, giving rise to an antiferromagnetic exchange interaction between the Co atoms. The magnetization measurements are well in line with the theoretical predictions, showing a dominating superparamagnetic behavior arising from small antiferromagnetic clusters containing uncompensated spins.

  • 217.
    Iusan, Diana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Bergqvist, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dederichs, P. H.
    Institute of Solid State Research, Research Center Juelich, D-525 25 Juelich, Germany.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Theoretical analysis of how high the ordering temperature of diluted magnetic semiconductors can becomeManuscript (preprint) (Other academic)
  • 218.
    Ivanov, Sergey A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Tellgren, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Ericsson, Tore
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Rundlöf, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Structural, magnetic and Mössbauer spectroscopic investigations of the magnetoelectric relaxor Pb(Fe0.6W0.2Nb0.2)O32007In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 9, no 5, p. 440-450Article in journal (Refereed)
    Abstract [en]

    The complex perovskite lead iron tungsten niobium oxide, Pb(Fe0.6W0.2Nb0.2)O3 (PFWN) which belongs to the class of disordered magnetoelectrics, has been studied by X-ray and neutron powder diffraction, magnetic and Mössbauer spectroscopic measurements. Structural, dielectric and magnetic properties of PFWN are presented and reviewed. Magnetic measurements indicate that the most important interactions are of antiferromagnetic nature yielding TN = 300 K, however, with indications of a reentrant spin glass behaviour below 20 K. The parameters of Mössbauer spectra also support the existence of the magnetic order and are consistent with the presence of high-spin Fe3+ cations located in the octahedral B-site. Rietveld refinements of diffraction data at different temperatures between 10 and 700 K have been carried out. The long-range structure of PFWN is cubic (space group Pm−3m) over the whole temperature interval. The Fe, W and Nb cations were found to be disordered over the perovskite B-sites. The Pb cations show a position disorder along the 111 direction shifting from their high-symmetry position. At the temperatures below TN, an antiferromagnetic arrangement of the magnetic moments of Fe3+ cations in the B-site is proposed in accordance with the antiferromagnetic properties of PFWN. The factors governing the observed nuclear and magnetic structures of PFWN are discussed and compared with those of pure Pb(Fe0.67W0.33)O3, Pb(Fe0.5Nb0.5)O3 and other quaternary Pb-based perovskites containing iron.

  • 219.
    Jafri, Hassan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Widenkvist, Erika
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Sanyal, Biplab
    Fransson, Jonas
    Eriksson, Olle
    Jansson, Ulf
    Grennberg, Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    The effect of induced vacancy defects on resistivity of graphene2009In: Scandem conference, Reykjavik 2009, 2009Conference paper (Refereed)
  • 220.
    Jafri, Syed Hassan Mujtaba
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Widenkvist, Erika
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Blom, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Experimental Physics.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
    Grennberg, Helena
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Biochemistry and Organic Chemistry.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Quinlan, Ronald A
    College of William and Mary, Williamsburg VA, USA.
    Holloway, Brian C
    Luna Innovations, Danville, VA, USA.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Conductivity engineering of graphene by defect formation2010In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 43, no 4, p. 045404-Article in journal (Refereed)
    Abstract [en]

    Transport measurements have revealed several exotic electronic properties of graphene. The possibility to influence the electronic structure and hence control the conductivity by adsorption or doping with adatoms is crucial in view of electronics applications. Here, we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, by more than one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by both quantum mechanical transport calculations as well as experimental studies of carbon nano-sheets. Our finding is attributed to the defect induced mid-gap states, which create a region exhibiting metallic behaviour around the vacancy defects. The modification of the conductivity of graphene by the implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics devices.

  • 221. Johansson, E. M. J.
    et al.
    Odelius, M.
    Gorgoi, M.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Ovsyannikov, R.
    Schafers, S.
    Svensson, Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Siegbahn, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Valence Electronic Structure Of Ruthenium Based Complexes Probed By Photoelectron Spectroscopy At High Kinetic Energy (Hike) And Modeled By Dft Calculations2008In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 464, no 4-6, p. 192-197Article in journal (Refereed)
    Abstract [en]

    The valence electronic structure of a series of molecular films containing ruthenium polypyridine complexes has been investigated by photoelectron spectroscopy (PES) at high kinetic energy (HIKE) using hard X-ray. The experiment shows the possibility to experimentally probe the metal contribution to the valence spectra in a bulk sensitive mode. Specifically to directly follow the Ru 4d contribution to the highest occupied molecular orbitals of such complexes. The experimental spectra are accurately modeled by DFT calculations only if a crystal structure environment is taken into account showing the importance of intermolecular interaction for modeling the electronic structure of such complexes.

  • 222.
    Johansson, E. M. J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Plogmaker, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Walle, L. E.
    Schölin, Rebecka
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Borg, A.
    Sandell, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Comparing Surface Binding of the Maleic Anhydride Anchor Group on Single Crystalline Anatase TiO2 (101), (100), and (001) Surfaces2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 35, p. 15015-15020Article in journal (Refereed)
    Abstract [en]

    We report on the surface binding of the maleic anhydride (C4H2O3, MA) on the TiO2 anatase (101), (100), and (001) single crystal surfaces. The MA anchor group has recently been used for dye adsorption in solar cells based on nanostructured anatase, and the results reported here are partly discussed with respect to such systems. MA was deposited simultaneously onto the (101), (100), and (001) TiO2 single crystal surfaces in UHV, and the surface binding was investigated with electron spectroscopy. The O1s and C1s core-level spectra were compared to a multilayer of MA to investigate the differences in bonding to the anatase surfaces. The results suggest a surface chemistry where the molecule reacts and the MA ring opens when adsorbed at the (101) and (100) surfaces. The molecule anchors via four oxygen atoms, similar to bonding with two carboxylic groups on TiO2. For the (001) surface, the spectra indicated a different adsorption geometry. A small amount of electronic states in the bandgap of the TiO2 surfaces was observed both before and after MA was deposited onto the surfaces, and on the (101) and (100) surfaces, the intensity of these surface states was slightly enhanced after deposition of MA.

  • 223.
    Johansson, LarsErik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bijelovic, Stojanka
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Eriksson, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Surpi, Alessandro
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Gothelid, Emmanuelle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Oscarsson, Sven
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    A magnetic microchip for controlled transport of attomole levels of proteins2010In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189, Vol. 10, no 5, p. 654-661Article in journal (Refereed)
    Abstract [en]

    A novel method of controlled transport of proteins immobilized on micrometre-sized magnetic beads in a lab-on-a-chip environment is presented. Bead motion is controlled by lithographically made magnetic elements forming transportation lines in combination with an applied in-plane rotating magnetic field. In this way, transport of attomole amounts of proteins is controlled with micrometre precision. Also, the activity of proteins immobilized on the beads is demonstrated by injecting antibodies into the system. A critical step in developing the method was to reduce sticking forces between beads and substrate during transportation of proteins. Charge interaction was found to be of minor importance compared to hydrophobic forces. To achieve a reliable transport of biologically active proteins, both substrate and beads were coated with polyethylene glycol (PEG) and the protein covered beads were suspended in buffer with surfactants. The described system fulfils all the important unit operations of a microfluidic platform and, as a further advantage, presents less need for microchannels and electric wiring.

  • 224.
    Jönsson, Petra E.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Superparamagnetism and Spin Glass Dynamics of Interacting Magnetic Nanoparticle Systems2004In: Advances in Chemical Physics, ISSN 0065-2385, E-ISSN 1934-4791, Vol. 128, p. 191-248Article, review/survey (Refereed)
  • 225.
    Jönsson, Petra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Takenaka, K
    Niitaka, S
    Sasagawa, T
    Sugai, S
    Takagi, H
    Correlation-driven heavy-fermion formation in LiV2O4.2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 16, p. 167402.1-167402.4Article in journal (Refereed)
    Abstract [en]

    Optical reflectivity measurements were performed on a single crystal of the d-electron heavy-fermion (HF) metal LiV2O4. Our results evidence the highly incoherent charge dynamics above T*≈20  K and the redistribution of the spectral weight of the optical conductivity over broad energy scales (∼5  eV) as the quantum coherence of the charge carriers is recovered. This reveals that LiV2O4 is close to a correlation-driven insulating state and indicates that, in sharp contrast to f-electron HF Kondo-lattice systems, strong electronic correlation effects dominate the heavy quasiparticle formation in LiV2O4

    .

  • 226. Kalvius, G. M.
    et al.
    Hartmann, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Krimmel, A.
    Wagner, F. E.
    Wäppling, Roger
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Tsurkan, V.
    Loidl, A.
    Krug von Nidda, H-A
    Spin-Lattice Instability in the Chromium Sulfur Spinel Fe0.5Cu0.5Cr2S42008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 25, p. 252204-Article in journal (Refereed)
    Abstract [en]

    Zero field mu SR spectroscopy was applied to a polycrystalline sample of the ferrimagnetic sulfur spinel Fe0.5Cu0.5Cr2S4 between 5 and 315 K. The temperature dependence of the interstitial magnetic field B-mu as well as the transverse and longitudinal relaxation rates were deduced. At around 100 K, the temperature dependence of the interstitial field exhibits a strong deviation from the expected Brillouin-like behavior together with a maximum of the transverse relaxation rate. These features are characteristic for a spin reorientation transition. This instability of the ferrimagnetic spin-lattice has not been reported previously. Fe-57 Mossbauer data from the same sample show no irregularity in the temperature dependence of the Fe hyperfine field which could indicate that the spin reorientation involves primarily the Cr sublattice. Above and below the spin reorientation regime, disorder in the spin-lattice is sizable, but not excessive. At low temperatures, the spins are essentially static, spin dynamics sets in above the reorientation range. The mu SR data are also complemented by new susceptibility and magnetization data taken on similar material.

  • 227. Kalvius, G. M.
    et al.
    Krimmel, A.
    Hartmann, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Litterst, F. J.
    Wäppling, Roger
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Tsurkan, V.
    Loidl, A.
    Magnetism of frustrated A-site spinels (Mn, Fe, Co)Al2O42009In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 404, no 5-7, p. 660-662Article in journal (Refereed)
    Abstract [en]

    In the A-site spinels MAl2O4 (M = Mn, Fe, Co) the A-site sublattice is subjected to strong frustration, putting all three compounds on the verge between long-range and short-range magnetic order. The mu SR spectra of the three compounds show two signals at all temperatures examined and a dramatic change in spectral shape at characteristic temperatures. Above this temperature, one signal (slowly relaxing) is typical for free paramagnetic spins, the other (fast relaxing) for highly correlated paramagnetic spins. For M = Mn the ratio of their intensities is 1:3 independent of temperature and the spectral change occurs around 40 K (T-N from neutron data) where the strongly correlated fraction enters into long-range order and the free paramagnetic fraction into a glassy spin state. For M = Co or Fe, the free paramagnetic fraction increases from similar to 20% to 85% with rising temperature. At the cusp temperatures observed in magnetization (5 or 12 K) the dominating, highly correlated paramagnetic fraction turns into a dynamic short-range ordered magnetic ground state. In all three compounds substantial local spin disorder and persistent spin fluctuations characterize their magnetic ground states, typical features of highly frustrated magnets.

  • 228. Kalvius, G. M.
    et al.
    Krimmel, A.
    Hartmann, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Wäppling, Roger
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Wagner, F. E.
    Litterst, F. J.
    Tsurkan, V.
    Loidl, A.
    Low temperature incommensurately modulated and noncollinear spin structure in FeCr2S42010In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 5, p. 052205-Article in journal (Refereed)
    Abstract [en]

    FeCr2S4 orders magnetically at T-N approximate to 170 K. According to neutron diffraction, the ordered state down to 4.2 K is a simple collinear ferrimagnet maintaining the cubic spinel structure. Later studies, however, claimed trigonal distortions below similar to 60 K coupled to the formation of a spin glass type ground state. To obtain further insight, muon spin rotation/relaxation (mu SR) spectroscopy was carried out between 5 and 200 K together with new Fe-57 Mossbauer measurements. Below similar to 50 K, our data point to the formation of an incommensurately modulated noncollinear spin arrangement like a helical spin structure. Above 50 K, the spectra are compatible with collinear ferrimagnetism, albeit with a substantial spin disorder on the scale of a few lattice constants. These spin lattice distortions become very large at 150 K and the magnetic state is now better characterized as consisting of rapidly fluctuating short-range ordered spins. The Neel transition is of second order, but ill defined, extending over a range of similar to 10 K. The Mossbauer data around 10 K confirm the onset of orbital freezing and are also compatible with the noncollinear order of iron. The absence of a major change in the quadrupole interaction around 50 K renders the distortion of crystal symmetry to be small.

  • 229. Kanchana, V
    et al.
    Vaitheeswaran, G
    Ma, Yanming
    Xie, Yu
    Svane, A
    Eriksson, O
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Density functional study of elastic and vibrational properties of the Heusler-type alloys Fe2VAl and Fe2VGa2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 12, p. 125108-Article in journal (Refereed)
    Abstract [en]

    The structural and elastic properties as well as phonon-dispersion relations of the Heusler-type alloys Fe2VAl and Fe2VGa are computed using density functional and density-functional perturbation theory within the generalized-gradient approximation. The calculated equilibrium lattice constants agree well with the experimental values. The elastic constants of Fe2VAl and Fe2VGa are predicted. From the elastic constants the shear modulus, Young's modulus, Poisson's ratio, sound velocities, and Debye temperatures are obtained. By analyzing the ratio between the bulk and shear moduli, we conclude that both Fe2VAl and Fe2VGa are brittle in nature. The computed phonon-dispersion relation shows that both compounds are dynamically stable in the L2(1) structure without any imaginary phonon frequencies. The isomer shifts in Fe in the two compounds are discussed in terms of the Fe s partial density of states, which reveal larger ionicity/less hybridization in Fe2VGa than in Fe2VAl. For the same reason the Cauchy pressure is negative in Fe2VAl but positive in Fe2VGa.

  • 230.
    Karis, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Svensson, Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Gorgoi, M.
    Schäfers, F.
    Braun, W.
    Eberhardt, W.
    Mårtensson, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    High-kinetic-energy photoemission spectroscopy of Ni at 1s: 6-eV satellite at 4 eV2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 23, p. 233105-Article in journal (Refereed)
    Abstract [en]

    Electron correlations are responsible for many profound phenomena in solid-state physics. A classical example is the 6-eV satellite in the photoelectron spectrum of Ni. Until now the satellite structure has only been investigated at the L shell and more shallow levels. Here we report a high-kinetic-energy photoemission spectroscopy (HIKE) investigation of Ni metal. We present 1s and 2p photoelectron spectra, obtained using excitation energies up to 12.6 keV. Our investigation demonstrates that the energy position of the satellite relative to the main line is different for the 1s and the 2p levels. In combination with electronic structure calculations, we show that this energy shift is attributed to unique differences in the core-valence coupling for the K and L2,3 shells in 3d transition metals, resulting in different screening of the core holes.

  • 231.
    Karlsson, E. B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Siegbahn, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
    Introduction to Kai Siegbahn's memorial issue2009In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 601, no 1-2, p. 1-7Article in journal (Refereed)
    Abstract [en]

    Kai Siegbahn is mainly known to the afterworld for his development of spectroscopies which have provided a detailed understanding of the electronic structure of atoms, molecules and condensed matter. These spectroscopies are based on the discoveries made by him and his collaborators in the beginning of the 1960s which led to a Nobel prize in physics for Kai in 1981. The collection of papers in the present volume illustrate the present status of the many flourishing aspects of electron spectroscopy which have developed as a result of his initial ideas and their background in nuclear physics experimentation. (C) 2009 Elsevier B.V. All rights reserved.

  • 232.
    Karlsson, Erik B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Coherent proton and deuteron states in neutron scattering2008In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 77, no 6, p. 065301-Article in journal (Refereed)
    Abstract [en]

    Neutron Compton scattering has been used for a long time as a method to obtain information about proton momentum distributions in organic molecules, metal hydrides, etc. However, in a number of recent papers it has been shown that scattering on protons (and to some extent also on deuterons) shows intensities that are much smaller than expected when compared to those of the other constituents of the measured systems. This has raised the question if the Compton scattering process is fully understood (do, for instance, electron excitations take up part of the recoil energy and momentum?) and casts doubts on the reliability of the method for its original purpose. The present paper presents a detailed explanation for the intensity deficits in a number of studied systems without involving any participation of a third body in the scattering process. It is a development of an earlier proposed model, in which the intensity loss is caused by destructive interference in the waves representing the scattered neutron and the recoiling particle. These interferences appear when the scattering particles are indistinguishable (and therefore in a quantum superposition state) when seen by the neutron. It requires that the neutron coherence length (which is determined by the energy selection) is comparable to the internuclear distances. It is shown that the latter condition is at least partially fulfilled for two, three or four particles in the experiments and that it is likely that the necessary coherence remains over the very short duration (femtosecond (fs)) of the scattering process. Quantitative agreement is obtained for several proton and deuteron containing systems, including the observed dependence of the intensity deficit on scattering angle, which is explained in terms of the actual recoil energy as related to the proton- or deuteron-binding energy in the different systems. The question of available final states for the scattering system is discussed.

  • 233.
    Karlsson, Erik B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Physics.
    Den komplicerade fotonen2008In: Fysik-aktuellt, ISSN 0283-9148, Vol. 3, p. 20-Article in journal (Refereed)
  • 234.
    Karlsson, P. G.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Göthelid, Emmanuelle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Richter, J. H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Sandel, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Initial stages of ZrO2 chemical vapor deposition on Si(100)-(2x1) from zirconium tetra-tert-butoxide2008In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, no 10, p. 1803-1809Article in journal (Refereed)
    Abstract [en]

    The initial stages of chemical vapor deposition of ZrO2 from zirconium tetra-tert-butoxide (ZTB) on Si(100)-(2 x 1) have been studied by scanning tunnelling microscopy (STM) and synchrotron radiation excited photoelectron spectroscopy (PES). The STM images and core level (PES) spectra indicate that the predominant surface modifications induced by ZTB are due to silicon carbonization and formation of zirconium dioxide. The carbonization reaction leads to formation of subsurface carbon and two types of reconstructions are discussed: dimer vacancies and dimer vacancies in conjunction with a rotated surface Si-dimer. Indications for the formation of small amounts of zirconium silicide are also found. No evidence for silicon oxidation can be observed with PES, in contrast to the interface properties previously found after larger exposures to ZTB.

  • 235.
    Karo, Jaanus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Structural Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    The Rôle of Side-Chains in Polymer Electrolytes for Batteries and Fuel Cells2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The subject of this thesis relates to the design of new polymer electrolytes for battery and fuel cell applications. Classical Molecular Dynamics (MD) modelling studies are reported of the nano-structure and the local structure and dynamics for two types of polymer electrolyte host: poly(ethylene oxide) (PEO) for lithium batteries and perfluorosulfonic acid (PFSA) for polymer-based fuel cells. Both polymers have been modified by side-chain substitution, and the effect of this on charge-carrier transport has been investigated. The PEO system contains a 89-343 EO-unit backbone with 3-15 EO-unit side-chains, separated by 5-50 EO backbone units, for LiPF6 salt concentrations corresponding to Li:EO ratios of 1:10 and 1:30; the PFSA systems correspond to commercial Nafion®, Hyflon® (Dow®) and Aciplex® fuel-cell membranes, where the major differences again lie in the side-chain lengths.

    The PEO mobility is clearly enhanced by the introduction of side-chains, but is decreased on insertion of Li salts; mobilities differ by a factor of 2-3. At the higher Li concentration, many short side-chains (3-5 EO-units) give the highest ion mobility, while the mobility was greatest for side-chain lengths of 7-9 EO units at the lower concentration. A picture emerges of optimal Li+-ion mobility correlating with an optimal number of Li+ ions in the vicinity of mobile polymer segments, yet not involved in significant cross-linkages within the polymer host.

    Mobility in the PFSA-systems is promoted by higher water content. The influence of different side-chain lengths on local structure was minor, with Hyflon® displaying a somewhat lower degree of phase separation than Nafion®. Furthermore, the velocities of the water molecules and hydronium ions increase steadily from the polymer backbone/water interface towards the centre of the proton-conducting water channels. Because of its shorter side-chain length, the number of hydronium ions in the water channels is ~50% higher in Hyflon® than in Nafion® beyond the sulphonate end-groups; their hydronium-ion velocities are also ~10% higher.

    MD simulation has thus been shown to be a valuable tool to achieve better understanding of how to promote charge-carrier transport in polymer electrolyte hosts. Side-chains are shown to play a fundamental rôle in promoting local dynamics and influencing the nano-structure of these materials.

    List of papers
    1. A molecular dynamics study of the effect of side-chains on mobility in a polymer host
    Open this publication in new window or tab >>A molecular dynamics study of the effect of side-chains on mobility in a polymer host
    2005 (English)In: Solid State Ionics, Vol. 176, no 39-40, p. 3041-3044Article in journal (Refereed) Published
    Abstract [en]

    The effect on polymer dynamics of adding methoxy-terminated poly(ethylene oxide) (PEO) side-chains with different lengths and separations to an amorphous long-chain PEO backbone has been studied by Molecular Dynamics (MD) simulation at 293 K and 330 K. The study is seen as having a direct general relevance to the optimal design of ion-conducting polymer hosts for both Li-ion battery and polymer fuel-cell applications. The MD box used contains a long-chain PEO backbone to which side-chains comprising 3, 6, 7, 8, 9 and 15 EO units are added. The chosen separations between the side-chains are 5, 10, 15, 20 and 50 EO units. All potentials used to describe these systems are taken from earlier work (J. Mater. Chem., 13 (2003) 214). The overall mobility of the polymer host system is found to have both minima and maxima at both temperatures for side-chain lengths in the range 6–9 EO units. This is almost totally independent of side-chain separation at 293 K, while the situation is more complex at 330 K.

    Keywords
    Molecular dynamics, Polymer side-chains, Chain separation, Ion conduction, Mobility, Polymer fuel cells
    National Category
    Inorganic Chemistry
    Identifiers
    urn:nbn:se:uu:diva-75441 (URN)doi:10.1016/j.ssi.2005.10.003 (DOI)
    Available from: 2006-02-07 Created: 2006-02-07 Last updated: 2011-01-11
    2. A Molecular Dynamics study of the influence of side-chain length and spacing on lithium mobility in non-crystalline LiPF6·PEOx; x = 10 and 30
    Open this publication in new window or tab >>A Molecular Dynamics study of the influence of side-chain length and spacing on lithium mobility in non-crystalline LiPF6·PEOx; x = 10 and 30
    2009 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 180, no 23-25, p. 1272-1284Article in journal (Refereed) Published
    Abstract [en]

    Molecular Dynamics (MD) simulation techniques have been used to investigate systematically how the length and spacing of poly(ethylene oxide) (PEO) side-chains along a PEO backbone influence ion mobility for two different salt concentrations. This is of fundamental relevance to the design of new polymer electrolytes for battery applications. The salt used has been LiPF6 in concentrations corresponding to Li:EO ratios of 1:30 and 1:10. The MD box contained PEO backbones of 89-343 EO units to which 3, 6, 7, 8, 9 and 15 EO unit side-chains were added. The selected spacings along the backbone between the PEO side-chains attachment points were 5, 10, 15, 20 and 50 EO units. The backbone and all side-chains were methoxy end-capped, and the simulations were all made at 293 K. Ion mobilities have been estimated from the variation of mean-square-displacement with time, and have been analysed in relation to chain dynamics, cross-linking and ion pairing. Comparisons are also made with the results of simulated PEO systems without side-chains and/or without salt. It is found that, at a higher concentration, many short side-chains give the highest ion mobility, while the mobility is highest for side-chain lengths of 7-9 EO units at the lower concentration.

    Keywords
    Molecular Dynamics; Ion conduction; Polymer electrolyte; Salt ions; Side-chain; Li-ion batteries
    National Category
    Inorganic Chemistry
    Research subject
    Inorganic Chemistry
    Identifiers
    urn:nbn:se:uu:diva-101259 (URN)10.1016/j.ssi.2009.07.009 (DOI)000273493500008 ()
    Available from: 2009-04-21 Created: 2009-04-21 Last updated: 2017-12-13Bibliographically approved
    3. Molecular dynamics studies of the Nafion®, Dow® and Aciplex® fuel-cell polymer membrane systems
    Open this publication in new window or tab >>Molecular dynamics studies of the Nafion®, Dow® and Aciplex® fuel-cell polymer membrane systems
    2007 (English)In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 13, no 10, p. 1039-1046Article in journal (Refereed) Published
    Abstract [en]

    The Nafion, Dow and Aciplex systems – where the prime differences lies in the side-chain length – have been studied by molecular dynamics (MD) simulation under standard pressure and temperature conditions for two different levels of hydration: 5 and 15 water molecules per (H)SO3 end-group. Structural features such as water clustering, water-channel dimensions and topology, and the dynamics of the hydronium ions and water molecules have all been analysed in relation to the dynamical properties of the polymer backbone and side-chains. It is generally found that mobility is promoted by a high water content, with the side-chains participating actively in the H3O+/H2O transport mechanism. Nafion, whose side-chain length is intermediate of the three polymers studied, is found to have the most mobile polymer side-chains at the higher level of hydration, suggesting that there could be an optimal side-chain length in these systems. There are also some indications that the water-channel network connectivity is optimal for high water-content Nafion system, and that this could explain why Nafion appears to exhibit the most favourable overall hydronium/water mobility.

    Keywords
    Molecular dynamics, Nafion membrane, Proton exchange membrane fuel cell (PEMFC), Side-chain length
    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-13970 (URN)10.1007/s00894-007-0230-7 (DOI)000248912300002 ()17665227 (PubMedID)
    Available from: 2008-01-28 Created: 2008-01-28 Last updated: 2018-01-03Bibliographically approved
    4. Molecular Dynamics Modelling of Proton Transport in Nafion® and Hyflon® Nano-Structures
    Open this publication in new window or tab >>Molecular Dynamics Modelling of Proton Transport in Nafion® and Hyflon® Nano-Structures
    (English)Manuscript (Other academic)
    Abstract
    Identifiers
    urn:nbn:se:uu:diva-101260 (URN)
    Available from: 2009-04-21 Created: 2009-04-21 Last updated: 2018-01-03
  • 236. Kastberg, Anders
    et al.
    Villemoes, Petrine
    Arnesen, Arne
    Heijkenskjöld, Filip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Langereis, Alexander
    Jungner, Peter
    Linneus, Staffan
    Transition probabilities in Sm II via optical nutation1993In: Z. Phys. D, Vol. 28, p. 285-288Article in journal (Refereed)
  • 237.
    Kim, Duck Young
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ab initio Lattice Dynamics: Hydrogen-dense and Other Materials2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents a theoretical study of materials under high pressure using ab initio lattice dynamics based on density functional theory and density functional perturbation theory using both super-cell and linear response approach.

    Ab initio lattice dynamics using super-cell approach is applied to compare our theoretical predictions with experimental findings. Phonon dispersion curves of fcc α-γ cerium are calculated and compared with inelastic X-ray scattering data. Pressure dependency of phonon density of states in two cubic phases TiO2 allows us to assign the observed cubic phase in experiments to be of fluorite rather than pyrite structure. Dynamical stability of cotunnite TiO2 phase at low pressure can explain the observed quenching phenomena in experiments. Our calculated O2 vibron mode in both ε-ζ phases of solid oxygen supports the hypothesis that both phases are iso-structural.

    Hydrogen-dense materials attract great attention not only because they open a path to study phenomena related to metallization (superconductivity) of solid hydrogen but also because they are closely related to important industrial applications (hydrogen storage). Using linear response method, we find that metallic fcc-AlH3 is dynamically stabilized in the range of 72-106 GPa and can persist at ambient pressure if finite temperature effects are considered. For SiH4, we test dynamical stability, Raman spectra, zero point energy, and utilize GW calculations for self energy correction. We find that a metallic tetragonal phase of SiH4 can be assigned to the experimentally observed one. Our ab initio lattice dynamics calculations based on density functional perturbation theory predict that fcc-YH3 is a pressure-induced superconductor with a high transition temperature of 40 K at 17.7 GPa. With increasing pressure this material undergoes a superconductor-metal-superconductor transition and the underlying mechanism of this transition can simultaneously explains also the observed metal-insulator transition at 25 GPa in YH3-δ.

    List of papers
    1. High-Temperature Superconductivity in the Hydrogen-Dense Transition Metal Hydride YH3
    Open this publication in new window or tab >>High-Temperature Superconductivity in the Hydrogen-Dense Transition Metal Hydride YH3
    (English)Article in journal (Refereed) Submitted
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-97981 (URN)
    Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2012-03-29Bibliographically approved
    2. Crystal structure of the pressure-induced metallic phase of SiH4 from ab initio theory
    Open this publication in new window or tab >>Crystal structure of the pressure-induced metallic phase of SiH4 from ab initio theory
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    2008 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 43, p. 16454-16459Article in journal (Refereed) Published
    Abstract [en]

    Metallization of pure solid hydrogen is of great interest, not least because it could lead to high-temperature superconductivity, but it continues to be an elusive goal because of great experimental challenges. Hydrogen-rich materials, in particular, CH4, SiH4, and GeH4, provide an opportunity to study related phenomena at experimentally achievable pressures, and they too are expected to be high-temperature superconductors. Recently, the emergence of a metallic phase has been observed in silane for pressures just above 60 GPa. However, some uncertainty exists about the crystal structure of the discovered metallic phase. Here, we show by way of elimination, that a single structure that possesses all of the required characteristics of the experimentally observed metallic phase of silane from a pool of plausible candidates can be identified. Our density functional theory and GW calculations show that a structure with space group P4/nbm is metallic at pressures > 60 GPa. Based on phonon calculations, we furthermore demonstrate that the P4/nbm structure is dynamically stable at > 43 GPa and becomes the ground state at 97 GPa when zero-point energy contributions are considered. These findings could lead the way for further theoretical analysis of metallic phases of hydrogen-rich materials and stimulate experimental studies.

    Keywords
    hydrogen-rich, metallization
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-97982 (URN)10.1073/pnas.0804148105 (DOI)000260913500012 ()
    Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2017-12-14Bibliographically approved
    3. Dynamical stability of the cubic metallic phase of AlH3 at ambient pressure: Density functional calculations
    Open this publication in new window or tab >>Dynamical stability of the cubic metallic phase of AlH3 at ambient pressure: Density functional calculations
    2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 10, p. 100102-Article in journal (Refereed) Published
    Abstract [en]

    We have characterized the high-pressure cubic phase of AlH3 from ab initio using density functional theory to determine mechanical as well as electronic properties and lattice dynamics (phonon-dispersion relations) from the response function method. Our zero-temperature phonon calculations show the softening of a particular mode with decreasing pressure, indicating the onset of a dynamic instability that continues to persist at ambient conditions. This instability can, however, be removed when finite electronic temperature effects are considered in the calculations. We furthermore identify a particular momentum transfer in the phonon-dispersion relation, matching a corresponding momentum transfer in the electronic band structure.

    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-97983 (URN)10.1103/PhysRevB.78.100102 (DOI)000259690400002 ()
    Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2017-12-14Bibliographically approved
    4. Cubic metallic phase of aluminum hydride showing improved hydrogen desorption
    Open this publication in new window or tab >>Cubic metallic phase of aluminum hydride showing improved hydrogen desorption
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    2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 20, p. 201903-Article in journal (Refereed) Published
    Abstract [en]

    Wereport on our results calculated from density functional theory andGW of the dehydrogenation properties in a cubic phase ofAlH3. The metallic nature of the electronic structure entails amore favorable hydrogen removal energy which is lowered by 75%compared to the insulating hexagonal phase. This remarkable reduction inthe Al–H bond strength bears important consequences for feasible applicationsof AlH3 as an on-board hydrogen storage material for mobileapplications. We suggest that the cubic phase could be preparedand stabilized experimentally at ambient pressure by off-board quenching.

    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-97984 (URN)10.1063/1.2931083 (DOI)000256196600017 ()
    Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2017-12-14Bibliographically approved
    5. On the dynamical stability and metallic behavior of YH3 under pressure
    Open this publication in new window or tab >>On the dynamical stability and metallic behavior of YH3 under pressure