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  • 301.
    Marcellini, Moreno
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Magnetic Ordering in Layered Magnets2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The preparation of layered magnets needs the knowledge of growth techniques which are focused on the growth of Fe/V(001) superlattices. Such films have been structurally investigated by X-rays reflectivity and diffraction.

    The magnetic investigations have been carried out by magneto-optic Kerr effect (MOKE), Superconducting Quantum Interference Device (SQUID) magnetometry and polarized neutron reflectivity (PNR). This latter technique has been used in cooperation with the Institute Laue Langvin (Grenoble, France) and Ruhr Universität (Bochum, Germany).

    The cross-over in universality class is shown in a series of layered magnets where a δ-doping layer of Fe has been embedded between two layers of Pd showing that the magnetization depends on the effective magnetic thickness of the polarized Pd. A model for the cross-over has been developed in terms of magnetic excitations.

    The interlayer exchange coupling (IEC) mediated by a non-magnetic spacer has been reviewed focusing the attention on the recent theoretical and experimental works based on Fe/V(001) superlattices.

    The IEC can be tailored at will by reversibly alloying of the spacer with H: this has been proved in Fe/V(001) double layers showing that in the two dimensional limit, the universality class is not affected by the coupling.

    The magnetic order-disorder transitions in Fe/V(001) superlattices do not seem to belong to any universality class. A phenomenological model which accounts for the effective coupling at the boundaries has been developed.

    The influence of the inherent ordering temperatures of single magnetic layers has been investigated in Fe/V(001) superlattices proving that the weakest ferromagnetic layer affects the overall magnetic ordering.

    A new kind of layered magnet has been developed to increase the effect of the boundaries. PNR measurements show that the universality class depends on which length-scale is investigated.

    Delarbeid
    1. Dimensionality crossover in the induced magnetization of Pd layers
    Åpne denne publikasjonen i ny fane eller vindu >>Dimensionality crossover in the induced magnetization of Pd layers
    Vise andre…
    2007 (engelsk)Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, nr 24, s. 246213-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The magnetic ordering of a series of samples consisting of ultrathin Fe layersembedded in Pd was investigated using the magneto-optical Kerr effect. Thesamples consisted of a single Fe layer with nominal thickness 0.2 dFe 1.6monolayers sandwiched between two 20 monolayer Pd layers. A dimensionalitycrossover from two dimensions to three dimensions occurs as dFe is increasedfrom 0.4 to 1.0 monolayers. First-principles calculations were performed inorder to determine the magnetic profile, and we used a spin-wave quantum wellmodel for obtaining a qualitative description of the dimensionality crossover.The results clearly prove the existence of a dimensionality crossover in theinduced magnetization, opening new routes for addressing the influence ofextension on order.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-95880 (URN)10.1088/0953-8984/19/24/246213 (DOI)000247074700028 ()
    Tilgjengelig fra: 2007-05-08 Laget: 2007-05-08 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    2. Oscillatory exchange coupling in the two-dimensional limit
    Åpne denne publikasjonen i ny fane eller vindu >>Oscillatory exchange coupling in the two-dimensional limit
    2005 (engelsk)Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, s. L477-483Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The dimensionality aspects of the order–disorder transition in single and double magnetic layers is addressed. A single Fe film of three monolayers, embedded in V(001) layers, was determined to be two-dimensional and XY-like. Two Fe layers, separated by 14.4 monolayers of V(001), were determined to belong to the same universality class as the single Fe film. The interlayer exchange coupling was altered in situ by introducing hydrogen in the V layers. An oscillation of the ordering temperature was observed, consistent with an oscillatory interlayer exchange coupling. The two-dimensional nature of the bilayer was confirmed by the ratio of the interlayer and intralayer couplings (). The results therefore support the existence of an oscillatory exchange coupling in the quasi-two-dimensional limit.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-95878 (URN)10.1088/0953-8984/17/44/L03 (DOI)
    Tilgjengelig fra: 2007-05-08 Laget: 2007-05-08 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    3. The influence of interlayer exchange coupling on the magnetic ordering in Fe/V superlattices
    Åpne denne publikasjonen i ny fane eller vindu >>The influence of interlayer exchange coupling on the magnetic ordering in Fe/V superlattices
    Vise andre…
    2009 (engelsk)Inngår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 321, nr 9, s. 1214-1220Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The relation between the interlayer exchange coupling and magnetic order is addressed, using Fe/V(0 0 1) superlattices as a model system. Large decrease in the ordering temperature (Tc) is observed with decreasing interlayer exchange coupling. The effective exponents of the magnetization were determined to be larger than 0.5 for all the samples, which is strongly deviating from the classical values of both two- and three-dimensional systems. This effect can partially be ascribed to the presence of boundaries, invoked by the finite number of magnetic layers.

    Emneord
    Magnetic superlattices, Magnetic phase transitions, Critical exponents
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-96975 (URN)10.1016/j.jmmm.2008.11.010 (DOI)000264170500022 ()
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    4. The influence of the distribution of the inherent ordering temperature on the ordering in layered magnets
    Åpne denne publikasjonen i ny fane eller vindu >>The influence of the distribution of the inherent ordering temperature on the ordering in layered magnets
    2009 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 14, s. 144426-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We study the influence of gradients in the inherent ordering temperature of coupled layered magnets on the overall magnetic ordering. The gradients were accomplished by growing Fe(001) layers with thicknesses ranging from two to three monolayers, all separated by   seven monolayers of V(001). Two types of gradient superstructures were grown: one with the highest and one with the lowest inherent ordering temperature in the center of the samples. The superstructure with the thinnest outermost Fe layers exhibits lower ordering temperature,  demonstrating the importance of the sequence of the layers. Both these   structures order at temperatures significantly lower than a superlattice with a constant thickness of the Fe layers (three monolayers). The results highlight the intricate collective aspects of  the magnetic ordering in layered magnets, which are not captured by current models in magnetism research.

    Emneord
    antiferromagnetic materials, ferromagnetic materials, iron, magnetic multilayers, monolayers, vanadium
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-96976 (URN)10.1103/PhysRevB.79.144426 (DOI)000265943200088 ()
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    5. The effect of boundaries on ordering in finite magnets
    Åpne denne publikasjonen i ny fane eller vindu >>The effect of boundaries on ordering in finite magnets
    (engelsk)Inngår i: Physical Review LettersArtikkel i tidsskrift (Fagfellevurdert) In press
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-96977 (URN)
    Tilgjengelig fra: 2008-04-02 Laget: 2008-04-02 Sist oppdatert: 2015-03-10bibliografisk kontrollert
  • 302.
    Marcellini, Moreno
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Pärnaste, Martin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Wolff, Maximilian
    The influence of the distribution of the inherent ordering temperature on the ordering in layered magnets2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 14, s. 144426-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the influence of gradients in the inherent ordering temperature of coupled layered magnets on the overall magnetic ordering. The gradients were accomplished by growing Fe(001) layers with thicknesses ranging from two to three monolayers, all separated by   seven monolayers of V(001). Two types of gradient superstructures were grown: one with the highest and one with the lowest inherent ordering temperature in the center of the samples. The superstructure with the thinnest outermost Fe layers exhibits lower ordering temperature,  demonstrating the importance of the sequence of the layers. Both these   structures order at temperatures significantly lower than a superlattice with a constant thickness of the Fe layers (three monolayers). The results highlight the intricate collective aspects of  the magnetic ordering in layered magnets, which are not captured by current models in magnetism research.

  • 303. Marinado, Tannia
    et al.
    Hagberg, Daniel P.
    Hedlund, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Edvinsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Johansson, Erik M. J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Boschloo, Gerrit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Rensmo, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Brinck, Tore
    Sun, Licheng
    Hagfeldt, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Rhodanine dyes for dye-sensitized solar cells: spectroscopy, energy levels and photovoltaic performance2009Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 1, s. 133-141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Three new sensitizers for photoelectrochemical solar cells were synthesized consisting of a triphenylamine donor, a rhodanine-3-acetic acid acceptor and a polyene connection. The conjugation length was systematically increased, which resulted in two effects: first, it led to a red-shift of the optical absorption of the dyes, resulting in an improved spectral overlap with the solar spectrum.Secondly, the oxidation potential decreased systematically. The excited state levels were, however, calculated to be nearly stationary. The experimental trends were in excellent agreement with density functional theory (DFT) computations. The photovoltaic performance of this set of dyes as sensitizers in mesoporous TiOredox couple. The dye with the best absorption characteristics showed the poorest solar cell efficiency, due to losses by recombination of electrons in TiOthe electrolyte led to a strongly reduced photocurrent for all dyes due to a reduced electron injection efficiency, caused by a 0.15 V negative shift of the TiO 2 solar cells was investigated using electrolytes containing the iodide/triiodide2 with triiodide. Addition of 4-tert butylpyridine to2 conduction band potential.

  • 304. Marinado, Tannia
    et al.
    Hahlin, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Jiang, Xiao
    Quintana, Maria
    Johansson, Erik M. J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Gabrielsson, Erik
    Plogmaker, Stefan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Hagberg, P
    Boschloo, Gerrit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Zakeeruddin, M
    Gratzel, Michael
    Siegbahn, Hans
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Sun, Licheng
    Hagfeldt, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Rensmo, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Surface Molecular Quantification and Photoelectrochemical Characterization of Mixed Organic Dye and Coadsorbent Layers on TiO2 for Dye-Sensitized Solar Cells2010Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 27, s. 11903-11910Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Different molecular layers on TiO2 were prepared by using the p-dimethylaniline triphenylamine based organic dye, D29, together with the coadsorbents decylphosphonic acid (DPA), dineohexyl bis(3,3-dimethylbutyl)phosphinic acid (DINHOP), and chenodeoxycholic acid (CDCA). The surface molecular structure of dye and coadsorbent layers on TiO2 was investigated by photoelectron spectroscopy (PES). A focus was to determine the surface molecular concentrations using characteristic photoelectron core levels. Dye-sensitized solar cells (DSCs) were prepared from the same substrate and were further characterized by photoelectrochemical methods. Together the investigation gives information on the arrangement of the mixed molecular layer and a first insight to the extent to which the coadsorbents exchange with dye molecules on the TiO2 surface for the examined conditions.

  • 305. Mattesini, M
    et al.
    Ahuja, R
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Sa, L
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Hugosson, H. W.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Johansson, B
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Eriksson, O
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Electronic structure and optical properties of solid C-602009Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 404, nr 12-13, s. 1776-1780Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure and the optical properties of face-centered-cubic C-60 have been investigated by using an all-electron full-potential method. Our ab initio results show that the imaginary dielectric function for high-energy values looks very similar to that of graphite, revealing close electronic structure similarities between the two systems. We have also identified the origin of different peaks in the dielectric function of fullerene by means of the calculated electronic density of states. The computed optical spectrum compares fairly well with the available experimental data for the Vis-UV absorption spectrum of solid C-60. (C) 2009 Elsevier B.V. All rights reserved.

  • 306. Mattesini, M
    et al.
    Buforn, E
    Udias, A
    Vitos, Levente
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    An ab initio study of S-substituted iron-nickel-silicon alloy at the Earth's inner core pressure2008Inngår i: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 28, nr 4, s. 437-441Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermodynamic stability of S-substituting Si into a bcc Fe0.80Ni0.05SxSi(0.15-x) random alloy, with x=0.025 n (n=0-- 4), was investigated up to 350GPa by using an ab initio density functional method based on the full charge density-exact muffin-tin orbital-coherent potential approximation scheme. From the analysis of the calculated H values, we suggest that the FeNiSSi stoichiometry with zero sulphur content always behaves as the most stable system along the whole pressure range of 0-350GPa. As a general tendency, we found that the alloys with 6.8-8.1wt.% Si are energetically more stable than those with lower silicon content, thus supporting the dissolution mechanism for the Earth's inner core compositional model.

  • 307. Mattesini, Maurizio
    et al.
    Belonoshko, Anatoly B.
    Buforn, Elisa
    Ramirez, Maria
    Simak, Sergei I.
    Udias, Agustin
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Hemispherical anisotropic patterns of the Earth's inner core2010Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, nr 21, s. 9507-9512Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves traveling similar to 3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth's inner core.

  • 308. Mattesini, Maurizio
    et al.
    Magnuson, Martin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Mjukröntgenfysik.
    Tasnadi, Ferenc
    Höglund, Carina
    Abrikosov, Igor
    Hultman, Lars
    Elastic properties and electrostructural correlations in ternary scandium-based cubic inverse perovskites: A first-principles study2009Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 79, s. 125122-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed ab initio calculations for the cubic inverse-perovskite Sc3EN E=Al,Ga, In systems tostudy their electronic band-structures and elastic properties. In this study, we used the accurate augmentedplane wave plus local orbital method to find the equilibrium structural parameters and to compute the fullelastic tensors. The obtained single-crystal elastic constants were used to quantify the stiffness of the Sc-basedternary nitrides and to appraise their mechanical stability. The site-projected density of states, Fermi surfaces,and the charge-density plots have also been used to analyze the chemical bonding between the Sc6N cluster andthe surrounding metallic lattice of either Al, Ga, or In atoms. Our calculations show that Sc3GaN has the largestcovalent Sc-N bonding-type character with the highest Young, shear, and bulk moduli. Compared with theother two isoelectronic systems, it also behaves as the most brittle material with a relatively large elasticanisotropy.

  • 309.
    Modin, Anders
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Yun, Younsuk
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Suzuki, Michi-To
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Vegelius, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Werme, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Nordgren, Joseph
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Oppeneer, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Butorin, Sergei
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Indication of single-crystal PuO2 oxidation from O 1s X-ray absorption spectraManuskript (Annet (populærvitenskap, debatt, mm))
  • 310.
    Mohanty, Jyoti
    et al.
    K. U. Leuven.
    Persson, Andreas
    Uppsala universitet. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Arvanitis, Dimitri
    Uppsala universitet. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Temst, Kristiaan
    K. U. Leuven.
    Van Haesendonck, Christian
    K. U. Leuven.
    Direct observation of frozen moments in the NiFe/FeMn exchange bias systemManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
  • 311. Moskalenko, S. A.
    et al.
    Liberman, M. A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Dumanov, V
    Stefan, G
    Shmiglyuk, M. I.
    Intra-Landau-level excitations of the two-dimensional electron-hole liquid2009Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 21, nr 23, s. 235801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The intra-Landau-level excitations of the two-dimensional electron-hole liquid are characterized by two branches of the energy spectrum. The acoustical plasmon branch with in-phase oscillations of electrons and holes has a linear dispersion law in the range of small wavevectors, with a velocity which does not depend on the magnetic field strength, and monotonically increases with saturation at higher values of the wavevectors. The optical plasmon branch with oscillations of electrons and holes in opposite phases has a quadratic dependence in the range of long wavelength, a weak roton-type behaviour at the intermediary values of the wavevectors and monotonically increases with saturation similar to the case of the acoustical branch. The influence of the supplementary in-plane electric field leads to the drift of the charged particles in the crossed electric and magnetic fields and to the energy spectrum as in the reference frame, where the e-h system is moving with the drift velocity. A perturbation theory using the Green function method is developed on the basis of a small parameter v(2)( 1 - v(2)), where v(2) is the filling factor and ( 1 - v(2)) displays the phase space filling effect.

  • 312. Moskalenko, S. A.
    et al.
    Liberman, Michael A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Dumanov, E. V.
    Collective Elementary Excitations of Two-Dimensional Magnetoexcitons in the Bose-Einstein Condensation State2009Inngår i: Journal of Nanoelectronics and Optoelectronics, ISSN 1555-130X, Vol. 4, nr 1, s. 52-75Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The collective elementary excitations of a system of two-dimensional magnetoexcitons in a state of Bose-Einstein condensation (BEC) with arbitrary wave vector was investigated in Hartree-Fock-Bogoliubov approximation. The breaking of the gauge symmetry of the Hamiltonian was introduced following the idea proposed by Bogoliubov in his theory of quasi-averages. The equations of motion were written in the frame of the starting electron and hole creation and annihilation operators. The chains of equations of motion for a set of Green's functions describing the exciton-type excitations as well as the plasmon-type excitations were deduced. Their disconnections were introduced using the perturbation theory with a small parameter of the theory proportional to the filling factor multiplied by the phase space filling factor. The energy spectrum of the collective elementary excitations is characterized by the interconnection of the exciton and plasmon branches, because the plasmon-type elementary excitations are gapless and are lying in the same spectral interval as the exciton-type elementary excitations.

  • 313. Mukhopadhyay, Saikat
    et al.
    Gowtham, S.
    Scheicher, Ralph H.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Pandey, Ravindra
    Karna, Shashi P.
    Theoretical study of physisorption of nucleobases on boron nitride nanotubes: a new class of hybrid nano-biomaterials2010Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, nr 16, s. 165703-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the adsorption of the nucleic acid bases-adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U)-on the outer wall of a high curvature semiconducting single-walled boron nitride nanotube (BNNT) by first-principles density functional theory calculations. The calculated binding energy shows the order: G > A approximate to C approximate to T approximate to U, implying that the interaction strength of the high curvature BNNT with the nucleobases, G being an exception, is nearly the same. A higher binding energy for the G-BNNT conjugate appears to result from hybridization of the molecular orbitals of G and the BNNT. A smaller energy gap predicted for the G-BNNT conjugate relative to that of the pristine BNNT may be useful in the application of this class of biofunctional materials to the design of next-generation sensing devices.

  • 314. Mulders, A. M.
    et al.
    Loosvelt, H.
    Fraile Rodriguez, A.
    Popova, E.
    Konishi, T.
    Temst, K.
    Karis, Olof
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Arvanitis, Dimitri
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
    Van Haesendonck, C.
    On The Interface Magnetism Of Thin Oxidized Co Films: Orbital And Spin Moments2009Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 21, nr 12, s. 124211-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An x-ray magnetic circular dichroism study of a polycrystalline Co/CoO   bilayer is presented. Using both the chemical specificity and surface   sensitivity in the core level techniques, we find that uncompensated   Co2+ spin moments participate in the remanent ferromagnetic response of   the bilayer that has oxygen nearest neighbors. These are likely located   at the Co/CoO interface. As intermixing of magnetic species is not   present in Co/CoO, it is concluded that the observed interface moments   are due to interface roughness. Given their direction, these moments   appear to not directly correlate to the exchange bias in these bilayers.

  • 315.
    Mårtensson, Nils
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Preobrajenski, A. B.
    Hennies, F.
    Bonding and dynamics of surface systems probed by soft X-rays2009Inngår i: The European Physical Journal - Special Topics, ISSN 1951-6355, Vol. 169, nr 1, s. 133-140Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    We review some aspects of the investigation of surface systems with soft X-rays. Examples are presented, showing how core level spectroscopies provide detailed information on the structure, bonding and chemistry of adsorbates and thin layers on surfaces. Core level spectroscopies employed at high brilliance synchrotron light sources allow furthermore access to electron dynamics in the attosecond domain, as we demonstrate for the core hole clock method.

  • 316.
    Ng, May Ling
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Preobrajenski, A. B.
    Vinogradov, A. S.
    Mårtensson, Nils
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Formation and temperature evolution of Au nanoparticles supported on the h-BN nanomesh2008Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, nr 6, s. 1250-1255Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sub-monolayers of gold have been grown at room temperature on the hexagonal boron nitride (h-BN) nanomesh formed on Rh(I 11)5 and studied systematically with core level and angle-resolved valence band photoelectron spectroscopy. The results are compared with those for the Au/Rh(111) and Au/h-BN/Pt(111) interfaces. It has been found that on clean Rh(111) substrate gold starts to grow two-dimensionally (21)), while in the presence of a h-BN interlayer it forms islands from the very beginning. In the case of flat h-BN monolayer (on Pt) these islands are essentially three-dimensional (31)) and irregular in size. In contrast, on the h-BN nanomesh (on Rh) gold grows initially as regular islands (predominantly 2D), probably filling the pores of the nanomesh. In addition, the evolution of the An islands in h-BN/Rh(111) upon annealing has been investigated with core level photoemission and X-ray absorption. The annealing at temperatures between RT and 300 degrees C does not affect the 2D character of Art islands, while further increase in temperature results in formation of 3D islands. At higher temperatures (above 500 degrees C), the gold atoms diffuse through h-13N into the Rh substrate and/or desorb from the surface. However, they do not influence the chemical bond between rhodium and h-BN at any stage of annealing: the nanomesh remains intact.

  • 317.
    Nilson, Katharina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Palmgren, Pål
    Åhlund, John
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Schiessling, Joachim
    Göthelid, Emmanuelle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Mårtensson, Nils
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Puglia, Carla
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Göthelid, Mats
    STM and XPS characterization of Zinc Phthalocyanine on InSb(001)2008Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 602, nr 2, s. 452-459Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Zinc phthalocyanine (ZnPc) adsorbed on the InSb(0 0 1)-c(8 x 2) surface has been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Coverages from sub-monolayer to monolayer (ML) have been investigated. The molecules form ordered structures on the reconstructed rows of the surface with the molecular plane parallel to the surface. A change in the electronic structure between the sub-ML and higher coverages has been observed. Moreover, in order to study the influence of annealing on the electronic and geometric structures, the samples have been heated to elevated temperatures (about 640 K). In addition, multi-layer ZnPc films have been characterized by XPS measurements.

  • 318.
    Nisar, J
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Scheicher, Ralph H.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Peng, X
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Stability of ferromagnetic phase in Fe-doped AlH32009Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 85, nr 6, s. 67006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have carried out a systematic theoretical investigation of Fe-doped AlH3 to study its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All calculations were performed using the projector augmented-wave method and generalized-gradient approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at 1.1 mu(B) per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms varying from 3.25 angstrom to 7.41 angstrom. We conclude that the ferromagnetic phase in Fe-doped AlH3 is stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due to the holes created by Fe-doping and the larger level splitting of the interacting gap states within the ferromagnetic phase. Copyright (C) EPLA, 2009

  • 319.
    Nisar, Jawad
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Araújo, C. Moysés
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Structural, electronic and energetic properties of water adsorbed on beta-Si3N4 (0001) surface: First-principles calculations2010Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 604, nr 5-6, s. 617-622Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structural, energetic and electronic properties of water molecules adsorbed on beta-Si3N4 (0 00 1) surface, at various coverages, are investigated using density functional theory. At low coverages (0 <= 0.5), it is found that all H2O molecules undergo spontaneous dissociation forming hydroxyl (OH) and imino (NH) groups where the reactive sites are identified, a result shown for the first time using ab initio theory. For higher coverages (0 > 0.5), only partial dissociation takes place where some of the molecules stay intact being bound via H-bond in good agreement with experimental findings. The driving force for the water dissociation has been identified to be dangling bonds on lower coordinated N and Si surface atoms showing that not all surface atoms are reactive corroborating with previous experimental findings. (C) 2010 Elsevier B.V. All rights reserved.

  • 320. Nissfolk, Jarl
    et al.
    Fredin, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Simiyu, Justus
    Häggman, Leif
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Hagfeldt, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Boschloo, Gerrit
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fysikalisk och analytisk kemi, Fysikalisk kemi.
    Interpretation of small-modulation photocurrent transients in dye-sensitized solar cells: A film thickness study2010Inngår i: Journal of Electroanalytical Chemistry, ISSN 1572-6657, Vol. 646, nr 1-2, s. 91-99Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron transport in dye-sensitized solar cells with varying mesoporous TiO2 film thicknesses was investigated using experimental and computational methods. More specifically, photocurrent transients resulting from small-amplitude square-wave modulation of the incident light were recorded for a series of solar cells, whereby the dependence of the wavelength and direction of the illumination was investigated. The responses were compared to simulations using different models for diffusional charge transport and analyzed in detail. The photocurrent transients are composed of two components: an initial fast response in case of illumination from the working electrode side, or an initial apparent delay of photocurrent decay for illumination from the counter electrode side, followed by a single exponential decay at longer times, with a time constant that is identified as the electron transport time. The initial response depends on the thickness and the absorption coefficient of the film. Transport times for different films were compared at equal short-circuit current density, rather than at equal light intensity. Experimentally, the transport time showed a power-law dependence on the film thickness with an exponent of about 1.5. Analysis using the quasi-static multiple trapping (MT) formulation demonstrates that this behavior originates from differences in quasi-Fermi level in the TiO2 films of different thickness when equal photocurrents are generated. The Fokker-Planck relation was used to derive expressions for the electrons flux in porous TiO2 films with a position-dependent diffusion coefficient.

  • 321.
    Nordström, Lars
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Calculation of technologically important aspects of magnetism: anisotropy, critical temperatures and spin dependent transport2008Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, nr 6, s. 064218-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Magnetic materials, where the moments arising from the electron spins are ordered, have many potential applications of technological relevance. For instance, in recent years the focus has been on spintronics, a future technology where not only the electron's charge but also its spin will be utilized. In this presentation we will deal with a few of these applications from a microscopic theoretical view. The discussion is based on calculations of the electronic structure often within (spin) density functional methods. A large magnetic anisotropy, the fact that there are considerable energy differences between different magnetization directions, has considerable importance for e. g. magnetic storage and permanent magnet applications. We will discuss here how to calculate this quantity, which is exemplified by both a bulk system and a layered material, and the calculational accuracy and the method's predictability. One example of spin dependent transport is the so-called spin transfer torque, the fact that a current through a magnetic layer can rotate its magnetization. We will review its physical origin and present some recent calculations on naturally magnetic layered materials, so-called helical spin density waves. A crucial quantity for applications of the various spectacular magnetic effects is the Curie temperature, the temperature above which the magnetic order disappears. Many systems are limited by low Curie temperatures. A route to calculations of this quantity is described, and with the help of a few calculations we try to generalize what is needed to achieve significant magnetic ordering temperatures.

  • 322. Nowak, G.
    et al.
    Zabel, H.
    Westerholt, I.
    Garfullin, M.
    Marcellini, Moreno
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Liebig, A.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Superconducting spin valves based on epitaxial Fe/V superlattices2008Inngår i: Physical review B. Condensed matter and materials physics, ISSN 1550-235X, Vol. 78, nr 13, s. 134520-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In superconducting spin valves of the type S/F1/N/F2 or F1/S/F2 with a superconducting layer S, two ferromagnetic layers F1 and F2, and a normal metallic layer N, the superconducting transition temperature T-S depends on the relative magnetization direction of the ferromagnetic layers F1 and F2. The difference of the transition temperature Delta T-S=T-s(AP)-T-s(P) with the magnetization direction of F1 and F2 either antiparallel or parallel is called the superconducting spin valve effect. We have prepared both types of spin valves by growing Fe/V thin-film heterostructures with epitaxial quality on MgO(001) substrates. In the S/F1/N/F2-type spin valves the ferromagnetic layers were the first two Fe layers of a [Fe/V] superlattice coupled antiferromagnetically via the interlayer exchange interaction. Here we observed a superconducting spin valve shift of up to Delta T-S approximate to 200 mK when aligning the sublattice magnetization in an external magnetic field. In the F1/S/F2-type spin valves the ferromagnetic layer F1 was either a [Fe/V] or a [FexV1-x/V] superlattice, the F2 layer was a Fe-, a Co-, or a FexV1-x film. Using weakly ferromagnetic FexV1-x alloy layers as F1 and F2 we find a spin valve effect of up to Delta T-S approximate to 20 mK, which is more than a factor of 2 larger than reported in the literature before for spin valves with comparable transition temperatures. Our results indicate that a high interface transparency and a large superconducting correlation length are prerequisites for the observation of a sizable superconducting spin valve effect.

  • 323. Nylander, Tommy
    et al.
    Campell, Richard
    Vandoolaeghe, Pauline
    Cárdenas, Marité
    Linse, Per
    Rennie, Adrian R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Neutron Reflectometry to Investigate the Delivery of Lipids and DNA to Interfaces2008Inngår i: Biointerphases, ISSN 1559-4106, Vol. 3, nr 2, s. FB64-FB82Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The application of scattering methods in the study of biological and biomedical problems is a field of research that is currently experiencing fast growth. In particular, neutron reflectometry (NR) is a technique that is becoming progressively more widespread, as indicated by the current commissioning of several new reflectometers worldwide. NR is valuable for the characterization of biomolecules at interfaces due to its capability to provide quantitative structural and compositional information on relevant molecular length scales. Recent years have seen an increasing number of applications of NR to problems related to drug and gene delivery. We start our review by summarizing the experimental methodology of the technique with reference to the description of biological liquid interfaces. Various methods for the interpretation of data are then discussed, including a new approach based on the lattice mean-field theory to help characterize stimulus-responsive surfaces relevant to drug delivery function. Recent progress in the subject area is reviewed in terms of NR studies relevant to the delivery of lipids and DNA to surfaces. Lastly, we discuss two case studies to exemplify practical features of NR that are exploited in combination with complementary techniques. The first case concerns the interactions of lipid-based cubic phase nanoparticles with model membranes (a drug delivery application), and the second case concerns DNA compaction at surfaces and in the bulk solution (a gene delivery application).

  • 324. Ohgai, T.
    et al.
    Enculescu, I.
    Zet, C.
    Westerberg, Lars
    Uppsala universitet, The Svedberg-laboratoriet.
    Hjort, Klas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Spohr, Reimar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Neumann, R.
    Magneto-sensitive nickel nanowires fabricated by electrodeposition into multi- and single-ion track templates2006Inngår i: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 36, nr 10, s. 1157-1162Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polycarbonate templates of ( 30 +/- 1) mu m thickness containing cylindrical etched-track nanochannels of ( 500 +/- 50) nm diameter were used for electrodeposition of Ni nanowires. Using 10(4) channels per cm(2), the most favourable deposition potential of -1.0 V was determined in a potentiostatic mode by varying the deposition potential with respect to an Ag/AgCl reference electrode over a range between -0.1 V and -1.5 V. The deposition efficiency at -1.0 V was estimated around 10%. The resulting single wires had a resistance around 200 W and showed an anisotropic magnetoresistance (AMR) effect of 1%, applicable to directionally sensitive magnetic field sensors.

  • 325. Olovsson, Weine
    et al.
    Marten, Tobias
    Holmström, Erik
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Abrikosov, Igor A.
    First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids2010Inngår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 178, s. 88-99Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a brief overview of recent theoretical studies of the core-level binding energy shift (CLS) in solid metallic materials. The focus is on first principles calculations using the complete screening picture, which incorporates the initial (ground state) and final (core-ionized) state contributions of the electron photoemission process in X-ray photoelectron spectroscopy (XPS), all within density functional theory (DFT). Considering substitutionally disordered binary alloys, we demonstrate that on the one hand CLS depend on average conditions, such as volume and overall composition, while on the other hand they are sensitive to the specific local atomic environment. The possibility of employing layer resolved shifts as a tool for characterizing interface quality in fully embedded thin films is also discussed, with examples for CuNi systems. An extension of the complete screening picture to core-core-core Auger transitions is given, and new results for the influence of local environment effects on Auger kinetic energy shifts in fcc AgPd are presented.

  • 326.
    Olsson, Ingrid U.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Radiocarbon Dating History: Early Days, Questions, and Problems Met2009Inngår i: Radiocarbon, ISSN 0033-8222, E-ISSN 1945-5755, Vol. 51, nr 1, s. 1-43Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    W F Libby's new dating method from the 1940s, based on experience in physics and chemistry, opened possibilities to check and revise chronologies built on other principles than radioactive decay. Libby's method initially implied collaboration with archaeologists to demonstrate that it worked but also with physicists to improve the technique to measure low beta-activities. Chemists, geophysicists, botanists, physiologists, statisticians, and other researchers have contributed to a prosperous interdisciplinary development. Some pitfalls were not recognized from the beginning, although issues such as contamination problems were foreseen by Libby. Pretreatment of samples was discussed very early by de Vries and collaborators. among others. This subject has not yet been abandoned. Closely related to pretreatment is the choice of fraction to be dated and chemicals to be used, especially for accelerator mass spectrometry(AMS) measurements. Calibration against tree rings and comparison with dates obtained using other methods as well as intercomparison projects are partly history but still very actual. The impact by man and climate is also studied since the early days of the method. Also, the carbon cycle has been of great interest. The tools for measurements and statistical analysis have been improved during these first 3 or 4 decades, allowing interpretations not possible earlier. delta C-13 determinations are mostly very important and useful, but sometimes they have been misleading in discussions of the origin of carbon. especially for human tissues-the metabolism was not yet fully understood. The history and development of the method can only be illustrated by selected examples in a survey like this.

  • 327.
    Oppeneer, Peter M.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Panchmatia, Pooja M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Sanyal, Biplab
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Eriksson, O.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ali, Md. Ehesan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Nature of the magnetic interaction between Fe-porphyrin molecules and ferromagnetic surfaces2009Inngår i: Progress in Surface Science, ISSN 0079-6816, E-ISSN 1878-4240, Vol. 84, nr 1-2, s. 18-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated computationally the magnetic spin state of free metalloporphyrins and how magnetic ordering in metalloporphyrins can be induced through contact with the metallic surface and what the origin of the exchange interaction is. To this end, we performed density functional theory (DFT) and DFT + U studies for a series of isolated, ligated as well as unligated Fe-porphyrin (FeP) molecules as well as various FeP molecules on surfaces. Our calculations for isolated FePs clearly demonstrate that the usual DFT-based exchange-correlation functionals (such as the generalized gradient approximation) cannot predict the experimental high-spin ground state of these molecules. Instead, one has to resort to DFT + U calculations with a Coulomb U of about 4 eV on the Fe atoms, to obtain the correct single-molecule spin state. The magnetic interaction between FeP and a Co surface has been studied computationally with the DFT and DFT + U approaches. Our total energy DFT and DFT + U calculations predict an optimal Fe - substrate distance of 3.5 angstrom and a ferromagnetic exchange coupling of FeP to the substrate, in accordance with recent experiments. For Fe-porphyrin chloride (FePCl), on the other hand, an antiferromagnetic coupling is computed to be more favorable. Our study demonstrates that due to an indirect exchange interaction, which is mediated through the four nitrogen atoms, ferromagnetic ordering on the FeP is stabilized.

  • 328.
    Ortiz, Carlos
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    First Principles Calculations of Electron Transport and Structural Damage by Intense Irradiation2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    First principle electronic structure theory is used to describe the effect of crystal binding on radiation detectors, electron transport properties, and structural damage induced by intense irradiation. A large database containing general electronic structure results to which data mining algorithms can be applied in the search for new functional materials, a case study is presented for scintillator detector materials. Inelastic cross sections for the generation of secondary electron cascades through impact ionization are derived from the dielectric response of an electron gas and evolved in time with Molecular Dynamics (MD). Qualitative and quantitive estimates are presented for the excitation and relaxation of a sample irradiated with Free Electron Laser pulses. A study is presented in where the structural damage on covalent bonded crystals following intense irradiation is derived from a Tight Binding approach and evolved in time with MD in where the evolution of the sample is derived from GW theory for the quasiparticle spectra and a dedicated Boltzmann transport equation for the impact ionization.

    Delarbeid
    1.
    Posten ble ikke funnet. Det kan skyldes at posten ikke lenger er tilgjengelig eller det er feil id i adressefeltet.
    2. Secondary Electron Cascade Dynamics in KI and CsI
    Åpne denne publikasjonen i ny fane eller vindu >>Secondary Electron Cascade Dynamics in KI and CsI
    2007 (engelsk)Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 46, s. 17442-17447Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We present a study of the characteristics of secondary electron cascades in two photocathode materials, KI and CsI. To do so, we have employed a model that enables us to explicitly follow the electron trajectories once the dielectric properties have been derived semiempirically from the energy loss function. Furthermore, we introduce a modification to the model by which the energy loss function is calculated in a first-principle manner using the GW approximation for the self-energy of the electrons. We find good agreement between the two approaches. Our results show comparable saturation times and secondary electron yields for the cascades in the two materials, and a narrower electron energy distribution (51%) for KI compared to that for CsI.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-102110 (URN)10.1021/jp0736692 (DOI)000251024500041 ()
    Tilgjengelig fra: 2009-05-06 Laget: 2009-05-05 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    3.
    Posten ble ikke funnet. Det kan skyldes at posten ikke lenger er tilgjengelig eller det er feil id i adressefeltet.
    4. Nanocrystal imaging using intense and ultrashort X-ray pulses
    Åpne denne publikasjonen i ny fane eller vindu >>Nanocrystal imaging using intense and ultrashort X-ray pulses
    Vise andre…
    (engelsk)Manuskript (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Structural studies of biological macromolecules are severely limited by radiation damage. Traditional crystallography curbs the effects of damage by spreading damage over many copies of the molecule of interest in the crystal. X-ray lasers offer an additional opportunity for limiting damage by out-running damage processes with ultrashort and very intense X-ray pulses. Such pulses may allow the imaging of single molecules, clusters or nanoparticles, but coherent flash imaging will also open up new avenues for structural studies on nano- and micro-crystalline substances. This paper addresses the potentials and limitations of nanocrystallography with extremely intense coherent X-ray pulses. We use urea nanocrystals as a model for generic biological substances, and simulate the primary and secondary ionization dynamics in the crystalline sample. The results establish conditions for diffraction experiments as a function of X-ray fluence, pulse duration, and the size of nanocrystals.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-102116 (URN)
    Tilgjengelig fra: 2009-06-25 Laget: 2009-05-05 Sist oppdatert: 2013-02-26bibliografisk kontrollert
    5. Radiation damage in covalent solids by intense ultra-short soft X-ray pulses
    Åpne denne publikasjonen i ny fane eller vindu >>Radiation damage in covalent solids by intense ultra-short soft X-ray pulses
    Vise andre…
    (engelsk)Manuskript (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Through irradiation with intense femtosecond soft X-ray pulses the structural damage originating from ultra-fast non-thermal phase transitions is observed. A computational model which combines electronic structure theory with molecular dynamics (MD) for the atomic motion is extended to include interactions relevant at soft X-ray wavelengths (6-13.5 nm). Dedicated Boltzmann transport equation is derived, with electron relaxation rates calculated from density functional theory and energy loss function from binary encounter theory. Preliminary results for diamond are presented and compared to the earlier predictions from MD simulations

    Identifikatorer
    urn:nbn:se:uu:diva-102121 (URN)
    Tilgjengelig fra: 2009-05-05 Laget: 2009-05-05 Sist oppdatert: 2010-01-14
  • 329.
    Ortiz, Carlos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Caleman, Carl
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för cell- och molekylärbiologi.
    Secondary Electron Cascade Dynamics in KI and CsI2007Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 46, s. 17442-17447Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a study of the characteristics of secondary electron cascades in two photocathode materials, KI and CsI. To do so, we have employed a model that enables us to explicitly follow the electron trajectories once the dielectric properties have been derived semiempirically from the energy loss function. Furthermore, we introduce a modification to the model by which the energy loss function is calculated in a first-principle manner using the GW approximation for the self-energy of the electrons. We find good agreement between the two approaches. Our results show comparable saturation times and secondary electron yields for the cascades in the two materials, and a narrower electron energy distribution (51%) for KI compared to that for CsI.

  • 330.
    Ortiz, Carlos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Klintenberg, Mattias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Data mining and accelerated electronic structure theory as a tool in the search for new functional materials2009Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 44, nr 4, s. 1042-1049Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A highly accelerated electronic structure implementation and data mining algorithms have been combined with structural data from the inorganic crystal structure database to generate materials properties for about 22,000 inorganic compounds. It is shown how data mining algorithms employed on the database can identify new functional materials with desired materials properties, resulting in a prediction of 136 novel materials with potential for use as detector materials for ionizing radiation. The methodology behind the automatized ab initio approach is presented, results are tabulated and a version of the complete database is made available at the internet web site

  • 331.
    Ortiz, Carlos
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Jeschke, Harald
    Gaudin, Jérôme
    Wang, Fenglin
    Weckert, Edgar
    Ziaja, Beata
    Radiation damage in covalent solids by intense ultra-short soft X-ray pulsesManuskript (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Through irradiation with intense femtosecond soft X-ray pulses the structural damage originating from ultra-fast non-thermal phase transitions is observed. A computational model which combines electronic structure theory with molecular dynamics (MD) for the atomic motion is extended to include interactions relevant at soft X-ray wavelengths (6-13.5 nm). Dedicated Boltzmann transport equation is derived, with electron relaxation rates calculated from density functional theory and energy loss function from binary encounter theory. Preliminary results for diamond are presented and compared to the earlier predictions from MD simulations

  • 332.
    Ottosson, Niklas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Aziz, E.
    Bergersen, Henrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Pokapanich, Wandared
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Öhrwall, Gunnar
    Svensson, Svante
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Eberhardt, W.
    Björneholm, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Electronic rearrangement upon the hydrolyzation of aqueous formaldehyde studied by core-electron spectroscopies2008Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, nr 51, s. 16642-16646Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have combined near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) to study the electronic rearrangement associated with the hydrolyzation of formaldehyde to methanediol in aqueous solution. The spectra are   contrasted against those of aqueous formamide and urea, which are structurally similar but do not undergo hydrolysis in solution. We have recently demonstrated that the hydrolyzation of formaldehyde is manifested in the oxygen Is NEXAFS spectrum by the disappearance of the oxygen 1s -> pi* absorption line. This is a characteristic signature   that the C=O double bond has been broken. In the present study we extend our investigation to include carbon Is NEXAFS and XPS spectra of the three solutions. The carbon NEXAFS spectra show the C 1s -> pi* absorption line for each solute except for formaldehyde. Moreover, the   carbon Is photoelectron spectra exhibit a single peak for each solute. These observations point to a near complete hydrolyzation of formaldehyde, whereas formamide and urea remain intact in the solution. The analysis is further supported by density functional theory (DFT) calculations, showing a C Is chemical shift of approximately 1.0 eV between hydrolyzed and nonhydrolyzed forms, which would give   distinguishable features in the photoemission spectrum, if coexisting forms were present in the solutions.

  • 333.
    Ottosson, Niklas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Aziz, E.
    Bradeanu, Ioana
    Legendre, Sebastian
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Öhrwall, Gunnar
    Svensson, Svante
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Björneholm, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Eberhardt, W.
    An electronic signature of hydrolysation in the X-ray absorption spectrum of aqueous formaldehyde2008Inngår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 460, nr 4-6, s. 540-542Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Formaldehyde in aqueous solution is hydrolysed and forms methanediol. Using X-ray absorption spectroscopy we show that the hydrolysation product can be identified by a distinct electronic signature in the spectra. This is manifested by the disappearance of the oxygen 1s -> ; pi* absorption line. The X-ray absorption spectrum of aqueous formaldehyde is compared with those of the structurally similar formamide and urea, which are in contrast not hydrolysed in aqueous solution. We thereby demonstrate the exceptional sensitivity and simplicity of the technique to monitor this fundamental process in the aqueous phase.

  • 334.
    Ottosson, Niklas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Vacha, Robert
    Aziz, Emad F.
    Pokapanich, Wandared
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Eberhardt, Wolfgang
    Svensson, Svante
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Öhrwall, Gunnar
    Jungwirth, Pavel
    Björneholm, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Winter, Bernd
    Large variations in the propensity of aqueous oxychlorine anions for the solution/vapor interface2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 12, s. 124706-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Core-level photoelectron spectroscopy measurements have been performed of aqueous solutions of NaCl codissolved with NaClOn (n=1-4). Each species has a distinct Cl 2p electron binding energy, which can be exploited for depth-profiling experiments to study the competition between Cl-and ClOn- anions for residing in the outermost layers of the solution/vapor interface. Strongest propensity for the surface is observed for n=4 (perchlorate), followed by n=3 (chlorate), n=2 (chlorite), n=0 (chloride), and n=1 (hypochlorite). Molecular dynamics simulations rationalize the greatest surface propensity of the most oxidized anions in terms of their larger size and polarizability. The anomalous behavior of hypochlorite, being less surface-active than chloride, although it is both larger and more polarizable, is suggested to arise from the charge asymmetry over the anion, increasing its efficiency for bulk solvation. (C) 2009 American Institute of Physics. [doi:10.1063/1.3236805]

  • 335. Paul, Amitesh
    et al.
    Sanyal, Biplab
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Chemical and magnetic interactions in Mn- and Fe-codoped Ge diluted magnetic semiconductors2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 21, s. 214438-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chemical and magnetic homogeneities of Mn and Fe, codoped in Ge, have been studied experimentally and theoretically. As we alter the codopant concentration in our diluted magnetic semiconductors, polarized neutron reflectivity measurements indicate no segregation and lower clustering tendencies for higher Fe doping. First-principles density-functional calculations based on Korringa-Kohn-Rostoker coherent-potential approximation show that Fe codoping introduces ferromagnetic interaction between Fe atoms as well as between Fe and Mn in contrast to only Mn-doped Ge. The clustering behavior observed in Mn-doped Ge is counteracted by the presence of Fe and hence increases the fraction of homogeneity, in agreement with the experiments. These observations indicate that Fe codoping makes Mn-doped Ge more attractive toward application.

  • 336.
    Peil, O. E.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ruban, A. V.
    Johansson, B.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ab initio study of atomic ordering and spin-glass transition in dilute CuMn alloys2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 2, s. 024428-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An archetypical spin-glass metallic alloy, Cu0.83Mn0.17, is studied by means of an ab initio based approach. First-principles calculations are employed to obtain effective chemical, strain-induced, and magnetic exchange interactions, as well as static atomic displacements, and the interactions are subsequently used in thermodynamic simulations. It is shown that the calculated atomic and magnetic short-range order accurately reproduces the results of neutron-scattering experiments. In particular, it is confirmed that the alloy exhibits a tendency toward ordering and the corresponding ordered phase is revealed. The magnetic structure is represented by spin-spiral clusters accompanied by weaker ferromagnetic short-range correlations. The spin-glass transition temperature obtained in Mont