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  • 251.
    Koči, L.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen, Kondenserade materiens teori (Fysik IV).
    Ahuja, R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Belonoshko, A. B.
    The impact of system restriction in molecular dynamics applied to the melting of Ne at high pressure2008Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 44, nr 2, s. 605-610Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There are two major ways to perform molecular dynamics (MD) calculations, namely classical and ab initio MD. As ab initio techniques require considerably longer calculation times, it is of interest to compare the results of the two methods. Furthermore, when melting is studied with MD, the use of coexistent solid and liquid structures (two-phase) in the calculations, instead of only a solid structure (one-phase), can have a substantial impact on the results   obtained. In this work, comparisons have been made between classical and ab initio methods applied to one- and two-phase systems for the melting of Ne at high pressure. The temperatures needed to melt the classical one-phase system are somewhat higher compared to the two-phase temperatures, evaluated at the same pressure. Furthermore,   there is a significant discrepancy comparing the one-phase ab initio curve to previously reported classical predictions. At 150 GPa, the calculations in this work show a melting temperature approximately 1000 K above the estimate based on an exponential-6 potential. However, there is a close match between the one-phase ab initio curve and the classical one-phase results in this work. This suggests a possible agreement between a two-phase ab initio and classical two-phase melting curve.

  • 252.
    Koči, L.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Kim, D. Y.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    de Almeida, J. S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Mattesini, M.
    Isaev, E.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Ahuja, R.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Mechanical stability of TiO2 polymorphs under pressure: ab initio calculations2008Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, nr 34, s. 345218-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First-principles calculations using plane-wave basis sets and ultrasoft pseudopotentials have been performed to study the mechanical stabilities of the rutile, pyrite, fluorite and cotunnite phases of titanium dioxide (TiO2). For these polymorphs, we have calculated the equilibrium volumes, equations of state, bulk moduli and selected elastic constants. Compared to the three phases rutile, pyrite and fluorite, the recently discovered cotunnite phase shows the highest c44 for all pressures considered. Cotunnite also shows the highest bulk modulus amongst the four studied phases at an ambient pressure of B0 = 272 GPa.

  • 253. Krisch, Michael
    et al.
    Farber, D. L.
    Xu, R.
    Antonangeli, Daniele
    Aracne, C. M.
    Beraud, Alexandre
    Chiang, Tai-Chang
    Zarestky, J.
    Kim, Duck Young
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Isaev, Eyvaz I.
    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 astronomi, Materialteori.
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Phonons of the anomalous element cerium2011Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, nr 23, s. 9342-9345Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many physical and chemical properties of the light rare-earths and actinides are governed by the active role of f electrons, and despite intensive efforts the details of the mechanisms of phase stability and transformation are not fully understood. A prominent example which has attracted a lot of interest, both experimentally and theoretically over the years is the isostructural gamma-alpha transition in cerium. We have determined by inelastic X-ray scattering, the complete phonon dispersion scheme of elemental cerium across the gamma -> alpha transition, and compared it with theoretical results using ab initio lattice dynamics. Several phonon branches show strong changes in the dispersion shape, indicating large modifications in the interactions between phonons and conduction electrons. This is reflected as well by the lattice Gruneisen parameters, particularly around the X point. We derive a vibrational entropy change Delta S-vib(gamma-alpha) approximate to (0.33 +/- 0.03)k(B), illustrating the importance of the lattice contribution to the transition. Additionally, we compare first principles calculations with the experiments to shed light on the mechanism underlying the isostructural volume collapse in cerium under pressure.

  • 254.
    Kristensen, Emma
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Fysiska institutionen.
    Larsson, Rolf
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi.
    Sánchez, Javier
    Uppsala universitet, Medicinska och farmaceutiska vetenskapsområdet, Medicinska fakulteten, Institutionen för onkologi, radiologi och klinisk immunologi, Enheten för klinisk immunologi.
    Rensmo, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Gelius, Ulrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Siegbahn, Hans
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Heparin coating durability on artificial heart valves studied by XPS and antithrombin binding capacity2006Inngår i: Colloids and Surfaces B: Biointerfaces, ISSN 0927-7765, E-ISSN 1873-4367, Vol. 49, nr 1, s. 1-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The durability and functionality of a heparin coating on artificial heart valve leaflets were evaluated with X-ray photoelectron spectroscopy (XPS) and by the coatings’ capacity to bind antithrombin. Current methods for accelerated life-time testing are based on exposing leaflets to water solutions. In this paper a method is explored, in which heart valve leaflets were exposed to a continuous high shear rate (4 L/min) of human citrated plasma. It was found that the heparin coating was stable and wear resistant enough to still be present after 3 weeks and to have about the same antithrombin uptake as coatings not exposed to circulating plasma. It was, however, partly destroyed by the test as found using XPS. We suggest that heparin chains from the upper layer of heparin have been torn off from the carrier chain, in combination with loss of heparin conjugate and plasma deposition in patches. This study showed that XPS provides additional information to biological measurements such as antithrombin uptake. XPS is therefore a valuable technique not only to characterize biomaterials but also to evaluate the effect of a performance test.

  • 255. Krylov, Boris
    et al.
    Morozov, Andrei
    Gerasimov, Gennady
    Arnesen, Arne
    Hallin, Reinhold
    Heijkenskjöld, Filip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Channels of energy transfer to atomic nitrogen in excited argon–nitrogen mixtures2002Inngår i: J. Phys. B, Vol. 35, s. 4257–4270-Artikkel i tidsskrift (Fagfellevurdert)
  • 256. Kvashnina, K. O.
    et al.
    Butorin, S. M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Mjukröntgenfysik.
    Cui, D.
    Vegelius, J.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Mjukröntgenfysik.
    Puranen, A.
    Gens, R.
    Glatzel, P.
    Electron transfer during selenium reduction by iron surfaces in aqueous solution: high resolution X-ray absorption study2009Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 190, nr 1, s. 012191-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a study of selenate (SeO42-) on an iron surface in ground water solution by X-ray absorption near-edge spectroscopy. Spectral sharpening is obtained by using the high energy resolution fluorescence detection technique that also efficiently suppresses the strong fluorescence signal from the Fe surface in the highly dilute samples (Se concentration < 3 ppm). We observe fully reduced Se on polished Fe surfaces while no changes are found for Se on oxidized Fe surface.

  • 257.
    Kádas, Krisztina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Lindquist, M
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Vitos, Levente
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Magnetism-driven anomalous surface alloying between Cu and Cr2009Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, nr 17, s. 172507-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cu-Cr contact materials are widely used as medium- and high-voltage vacuum interrupters. The microstructure of these materials is critical in their performance: the finer structure they have, the better are their physical properties. A solid solution of Cu and Cr could significantly increase the performance of such contact materials. However, Cu and Cr are practically immiscible in the bulk phase. Based on first principles density functional theory we show here that the solubility of Cr in Cu is dramatically increased on Cu surfaces already at room temperature and Cu-Cr alloys are formed on both the Cu(111) and Cu(100) surfaces. We demonstrate that the origin of this phenomenon is the unique magnetic properties of Cr atoms near surfaces.

  • 258.
    Kádas, Krisztina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Vitos, Levente
    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.
    Elastic properties of iron-rich hcp Fe-Mg alloys up to Earth's core pressures2008Inngår i: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 271, nr 1-4, s. 221-225Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using density functional theory formulated within the framework of the exact muffin-tin orbital method, we investigate the elastic properties of hexagonal closed-packed Fe-Mg alloys, containing 5 and 10 at.% Mg, up to pressures of the Earth's inner core. We demonstrate the effect of Mg alloying on the hexagonal axial ratio, elastic constants, density and sound wave velocities. We find that 10% Mg alloying decreases the shear modulus of iron by 23% and reduces the transverse sound velocity, nu(s) by 12% at core pressures. Although it is debated whether or not Mg can partition into the core, our results support Mg as a candidate light element in the core.

  • 259.
    Kádas, Krisztina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Vitos, Levente
    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.
    Theoretical evidence of a superconducting transition in doped silicon and germanium driven by a variation of chemical composition2008Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, nr 5, s. 052505-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the first theoretical evidence of chemical composition driven superconductivity in acceptor-doped silicon and germanium, using density functional theory. We examine the concentration dependence of T-c in B-doped Si and Ge and predict that B-doped Ge is a superconductor with a slightly higher T-c than B-doped Si. We show that there is a critical concentration above which B-doped Si and Ge become superconducting and estimate it to be similar to 2.6% in Si:B and similar to 2.2% in Ge:B. Considering the Al-doped Si and Ge, we point out the decisive role of the chemical element in the hole-doping scenario.

  • 260.
    Kádas, Krisztina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Vitos, Levente
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Johansson, Börje
    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 body-centered cubic iron-magnesium alloys in the Earth's inner core2009Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, nr 37, s. 15560-15562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The composition and the structure of the Earth's solid inner core are still unknown. Iron is accepted to be the main component of the core. Lately, the body-centered cubic (bcc) phase of iron was suggested to be present in the inner core, although its stability at core conditions is still in discussion. The higher density of pure iron compared with that of the Earth's core indicates the presence of light element(s) in this region, which could be responsible for the stability of the bcc phase. However, so far, none of the proposed composition models were in full agreement with seismic observations. The solubility of magnesium in hexagonal Fe has been found to increase significantly with increasing pressure, suggesting that Mg can also be an important element in the core. Here, we report a first-principles density functional study of bcc Fe-Mg alloys at core pressures and temperatures. We show that at core conditions, 5-10 atomic percent Mg stabilizes the bcc Fe both dynamically and thermodynamically. Our calculated density, elastic moduli, and sound velocities of bcc Fe-Mg alloys are consistent with those obtained from seismology, indicating that the bcc-structured Fe-Mg alloy is a possible model for the Earth's inner core.

  • 261. Landa, A
    et al.
    Soderlind, P
    Ruban, V
    Peil, E
    Vitos, Levente
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Stability in bcc Transition Metals: Madelung and Band-Energy Effects due to Alloying2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, nr 23, s. 235501-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The phase stability of group VB (V, Nb, and Ta) transition metals is explored by first-principles electronic-structure calculations. Alloying with a small amount of a neighboring metal can either stabilize or destabilize the body-centered-cubic phase relative to low-symmetry rhombohedral phases. We show that band-structure effects determine phase stability when a particular group VB metal is alloyed with its nearest neighbors within the same d-transition series. In this case, the neighbor with less (to the left) and more (to the right) d electrons destabilize and stabilize bcc, respectively. When alloying with neighbors of higher d-transition series, electrostatic Madelung energy dominates and stabilizes the body-centered-cubic phase. This surprising prediction invalidates current understanding of simple d-electron bonding that dictates high-symmetry cubic and hexagonal phases.

  • 262.
    Landström, Lars
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi.
    Lu, Jun
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Heszler, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Size-Distribution and Emission Spectroscopy of W Nanoparticles Generated byLaser-Assisted CVD for Different WF6/H2/Ar Mixtures2003Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, nr 42, s. 11615-11621Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tungsten nanoparticles were produced by ArF excimer laser-assisted chemical vapor deposition fromWF6/H2/Ar gas mixtures. Subsequent pulses excited the gas-phase particles, allowing optical emissionspectroscopy to monitor the intensity of the emitted radiation and temperature of the laser-heated particles.A systematic study on size-distributions of the deposited particles, determined by electron microscopy, inconnection with emission spectroscopy and rate of deposition measurements is presented, with respect todifferent partial pressures of the reactants. The rates of deposition of W nanoparticle films were determinedby X-ray fluorescence spectroscopy. In addition, the intensity of the scattered 193 nm laser line was alsomonitored as the partial pressure of H2 was varied.

  • 263.
    Larsson, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Computational Studies of Nanotube Growth, Nanoclusters and Cathode Materials for Batteries2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Density functional theory has been used to investigate cathode materials for rechargeable batteries, carbon nanotube interactions with catalyst particles and transition metal catalyzed hydrogen release in magnesium hydride nanoclusters.

    An effort has been made to the understand structural and electrochemical properties of lithium iron silicate (Li2FeSiO4) and its manganese-doped analogue. Starting from the X-ray measurements, the crystal structure of Li2FeSiO4 was refined, and several metastable phases of partially delithiated Li2FeSiO4 were identified. There are signs that manganese doping leads to structural instability and that lithium extraction beyond 50% capacity only occurs at impractically high potentials in the new material.

    The chemical interaction energies of single-walled carbon nanotubes and nanoclusters were calculated. It is found that the interaction needs to be strong enough to compete with the energy gained by detaching the nanotubes and forming closed ends with carbon caps. This represents a new criterion for determining catalyst metal suitability. The stability of isolated carbon nanotube fragments were also studied, and it is argued that chirality selection during growth is best achieved by exploiting the much wider energy span of open-ended carbon nanotube fragments.

    Magnesium hydride nanoclusters were doped with transition metals Ti, V, Fe, and Ni. The resulting changes in hydrogen desorption energies from the surface were calculated, and the associated changes in the cluster structures reveal that the transition metals not only lower the desorption energy of hydrogen, but also seem to work as proposed in the gateway hypothesis of transition metal catalysis.

    Delarbeid
    1. An ab initio study of the Li-ion battery cathode material Li2FeSiO4
    Åpne denne publikasjonen i ny fane eller vindu >>An ab initio study of the Li-ion battery cathode material Li2FeSiO4
    2006 (engelsk)Inngår i: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 8, nr 5, s. 797-800Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A density functional theory (DFT) calculation is reported for the novel Li-ion battery cathode material lithium iron silicate (Li2FeSiO4) and for three possible Li arrangements in the delithiated structure (LiFeSiO4). Relevant battery-related properties have been derived: average voltage (2.77 V vs. Li/Li+), energy density (1200 Wh/l) and specific energy (440 Wh/kg). Lattice constants and atomic fractional coordinates are also given for each case. The calculated values are in good agreement with recent experimental values (A. Nytén, A. Abouimrane, M. Armand, T. Gustafsson, J.O. Thomas, Electrochem. Commun., 7 (2005) 156). Voltages were calculated (again vs. Li/Li+) for the three different Li arrangements in LiFeSiO4; these differed by 0.22 V – a difference which could perhaps be related to the experimentally observed 0.30 V drop in voltage between the first and subsequent charge cycles.

    Emneord
    Li2FeSiO4, Lithium iron silicate, Cathode material, Li-ion battery, Density functional theory
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-94467 (URN)10.1016/j.elecom.2006.03.012 (DOI)
    Tilgjengelig fra: 2006-04-21 Laget: 2006-04-21 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    2. Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations
    Åpne denne publikasjonen i ny fane eller vindu >>Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations
    2009 (engelsk)Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 4, s. 043510-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this paper, we report on Na2FePO4F and Li2FePO4F, which are materials that are used as cathodes in batteries, using density functional theory with the LDA, LDA + U, GGA, or GGA + U approximations. Specifically, we study their crystal structure, electronic structure, and magnetic properties and provide similar information about the intermediate compounds LiFePO4F and NaFePO4F. Finally, the intercalation voltages of the corresponding batteries are calculated using various exchange-correlation approximations and conclusions are drawn about which one is the most suitable to use for the study of this class of materials.

    sted, utgiver, år, opplag, sider
    American Institute of Physics, 2009
    HSV kategori
    Forskningsprogram
    Materialvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-108262 (URN)10.1063/1.3202384 (DOI)000270083800025 ()
    Tilgjengelig fra: 2009-09-10 Laget: 2009-09-10 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    3. Calculating carbon nanotube–catalyst adhesion strengths
    Åpne denne publikasjonen i ny fane eller vindu >>Calculating carbon nanotube–catalyst adhesion strengths
    Vise andre…
    2007 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 11, s. 115419-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Density-functional theory is used to assess the validity of modeling metal clusters as single atoms or rings of atoms when determining adhesion strengths between clusters and single-walled carbon nanotubes (SWNTs). Representing a cluster by a single atom or ring gives the correct trends in SWNT-cluster adhesion strengths (Fe ≈ Co > Ni), but the single-atom model yields incorrect minimum-energy structures for all three metals. We have found that this is because of directional bonding between the SWNT end and the metal cluster, which is captured in the ring model but not by the single atom. Hence, pairwise potential models that do not describe directional bonding correctly, and which are commonly used to study these systems, are expected to give incorrect minimum-energy structures.

    HSV kategori
    Forskningsprogram
    Materialvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-108263 (URN)10.1103/PhysRevB.75.115419 (DOI)000245329600124 ()
    Tilgjengelig fra: 2009-09-10 Laget: 2009-09-10 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    4. The importance of strong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubes
    Åpne denne publikasjonen i ny fane eller vindu >>The importance of strong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubes
    Vise andre…
    2008 (engelsk)Inngår i: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, nr 2, s. 463-468Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Density functional theory is used to show that the adhesion between single-walled carbon nanotubes (SWNTs) and the catalyst particles from which they grow needs to be strong to support nanotube growth. It is found that Fe, Co, and Ni, commonly used to catalyze SWNT growth, have larger adhesion strengths to SWNTs than Cu, Pd, and Au and are therefore likely to be more efficient for supporting growth. The calculations also show that to maintain an open end of the SWNT it is necessary that the SWNT adhesion strength to the metal particle is comparable to the cap formation energy of the SWNT end. This implies that the difference between continued and discontinued SWNT growth to a large extent depends on the carbon-metal binding strength, which we demonstrate by molecular dynamics (MD) simulations. The results highlight that first principles computations are vital for the understanding of the binding strength's role in the SWNT growth mechanism and are needed to get accurate force field parameters for MD.

    HSV kategori
    Forskningsprogram
    Materialvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-108264 (URN)10.1021/nl072431m (DOI)000253166200016 ()18162001 (PubMedID)
    Tilgjengelig fra: 2009-09-10 Laget: 2009-09-10 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    5. Copper/Molybdenum Nanocomposite Particles as Catalysts for the Growth of Bamboo-Structured Carbon Nanotubes
    Åpne denne publikasjonen i ny fane eller vindu >>Copper/Molybdenum Nanocomposite Particles as Catalysts for the Growth of Bamboo-Structured Carbon Nanotubes
    Vise andre…
    2008 (engelsk)Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, nr 32, s. 12201-12206Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Bamboo-structured carbon nanotubes (BCNTs), with mean diameters of 20 nm, have been synthesized on MgO-supported Cu and Mo catalysts by the catalytic chemical vapor deposition of methane. BCNTs could only be generated using a combination of Cu and Mo catalysts. No BCNTs were produced from either individual Cu or Mo catalysts. In combination, Mo was found to be essential for cracking the methane precursor, while Cu was required for BCNT formation. Energy dispersive X-ray analysis of the individual particles at the tips of the nanotubes suggest that Cu and Mo are present as a “composite” nanoparticle catalyst after growth. First-principles modeling has been used to describe the interaction of the Cu/Mo catalyst with the nanotubes, suggesting that the catalyst binds with the same energy as traditional catalysts such as Fe, Ni, and Co.

    HSV kategori
    Forskningsprogram
    Materialvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-108265 (URN)10.1021/jp8023556 (DOI)000258290100026 ()
    Tilgjengelig fra: 2009-09-10 Laget: 2009-09-10 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    6. Role of Catalyst in Dehydrogenation of MgH2 Nanoclusters
    Åpne denne publikasjonen i ny fane eller vindu >>Role of Catalyst in Dehydrogenation of MgH2 Nanoclusters
    Vise andre…
    2008 (engelsk)Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, nr 24, s. 8227-8231Artikkel i tidsskrift (Fagfellevurdert) Published
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-96881 (URN)10.1073/pnas.0711743105 (DOI)
    Tilgjengelig fra: 2008-03-20 Laget: 2008-03-20 Sist oppdatert: 2017-12-14bibliografisk kontrollert
  • 264.
    Larsson, Peter
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Liivat, Anti
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Thomas, John O.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Strukturkemi.
    Structural and electrochemical aspects of Mn substitution into Li2FeSiO4 from DFT calculations2010Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, nr 3, s. 678-684Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    DFT calculations are presented which probe the effect of low-concentration Mn substitution of the Fe-sites in Li2FeSiO4: the promising new and potentially cheap cathode material for upscaled Li-ion battery applications. The LixFe0.875Mn0.125SiO4 System investigated could be achieved by replacing 12.5% of the Fe-sites in 2 x 2 x 1 and 2 x 2 x 2 supercells by Mn ions. The evolution of Bader charges and partial densities of states (DOS) have been followed under a stepwise delithiation process. A clear structural distortion is seen to occur at the Mn-site on delithiation, suggesting possible structural instability. Oxidation of Mn beyond 3+ is calculated to occur at potentials in excess of 4.7 V, implying that oxidation of well separated (>10 angstrom) low-concentration Mn ions to Mn4+ is energetically unfavourable in the LixFe0.875Mn0.125SiO4 structure. This, together with previous DFT results for higher levels of Mn substitution into Li2FeSiO4, indicates that capacity increase in Li2Fe1 (-) yMnySiO4 through a > 1 electron redox reaction may not be so readily attainable in practice, either for high or low Mn concentrations.

  • 265.
    Larsson, Peter
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Araújo, C. Moysés
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Larsson, J. Andreas
    Jena, Puru
    Ahuja, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Role of Catalyst in Dehydrogenation of MgH2 Nanoclusters2008Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, nr 24, s. 8227-8231Artikkel i tidsskrift (Fagfellevurdert)
  • 266. Laukkanen, P.
    et al.
    Punkkinen, M. P. J.
    Ahola-Tuomi, M.
    Lang, J.
    Schulte, K.
    Pietzsch, A.
    Kuzmin, M.
    Sadowski, J.
    Adell, J.
    Perala, R. E.
    Ropo, M.
    Kokko, K.
    Vitos, Levente
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Johansson, Börje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Pessa, M.
    Vayrynen, I. J.
    Core-level shifts of the c(8 x 2)-reconstructed InAs(100) and InSb(100) surfaces2010Inngår i: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 177, nr 1, s. 52-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have studied In-stabilized c(8 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) semiconductor surfaces, which play a key role in growing improved III-V interfaces for electronics devices, by core-level photoelectron spectroscopy and first-principles calculations. The calculated surface core-level shifts (SCLSs) for the zeta and zeta a models, which have been previously established to describe the atomic structures of the III-V(1 00)c(8 x 2) surfaces, yield hitherto not reported interpretation for the As 3d, In 4d, and Sb 4d core-level spectra of the III-V(1 00)c(8 x 2) surfaces, concerning the number and origins of SCLSs. The fitting analysis of the measured spectra with the calculated zeta and zeta a SCLS values shows that the InSb spectra are reproduced by the zeta SCLSs better than by the zeta a SCLSs. Interestingly, the zeta a fits agree better with the InAs spectra than the zeta fits do, indicating that the zeta a model describes the InAs surface better than the InSb surface. These results are in agreement with previous X-ray diffraction data. Furthermore, an introduction of the complete-screening model, which includes both the initial and final state effects, does not improve the fitting of the InSb spectra, proposing the suitability of the initial-state model for the SCLSs of the III-V(1 0 0)c(8 x 2) surfaces. The found SCLSs are discussed with the ab initio on-site charges. (C) 2010 Elsevier B.V. All rights reserved.

  • 267.
    Lawniczak-Jablonska, Krystyna
    et al.
    Polish Academy of Sciences, Warsaw.
    Wolska, Anna
    Polish Academy of Sciences, Warsaw.
    Bak-Misiuk, Jadwiga
    Polish Academy of Sciences, Warsaw.
    Dynowska, Elzbieta
    Polish Academy of Sciences, Warsaw.
    Romanowski, Przemyslaw
    Polish Academy of Sciences, Warsaw.
    Domagala, Jaroslaw Z.
    Polish Academy of Sciences, Warsaw.
    Minikayev, Roman
    Polish Academy of Sciences, Warsaw.
    Wasik, Dariusz
    University of Warsaw.
    Klepka, Marcin T.
    Polish Academy of Sciences, Warsaw.
    Sadowski, Janusz
    Polish Academy of Sciences, Warsaw.
    Barcz, Adam
    Polish Academy of Sciences, Warsaw.
    Dluzewski, Piotr
    Polish Academy of Sciences, Warsaw.
    Kret, Sławomir
    Polish Academy of Sciences, Warsaw.
    Twardowski, Andrzej
    University of Warsaw.
    Kamińska, Maria
    University of Warsaw.
    Persson, Andreas
    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.
    Holub-Krappe, Elisabeth
    Helmholtz Centre Berlin for Materials and Energy.
    Kwiatkowski, Adam
    University of Warsaw.
    Structural and magnetic properties of the molecular beam epitaxy grown MnSb layers on GaAs substrates2009Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, nr 8, s. 083524-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structural and magnetic properties of MnSb layers grown on two   differently oriented GaAs substrates are reported. The MnSb compounds   grow nonhomogenously both on GaAs (111) B and on GaAs (100) substrates.   In x-ray diffraction studies the formation of two epitaxial domains is   observed depending on the crystallographic orientation of the   substrate. The observed diffusion of Ga atoms from the substrate to the   layers results in the formation of an additional Mn-rich cubic phase of   GaMnSb. In the case of the (100) oriented substrate, the diffusion of   Mn into the substrate was additionally found. Traces of other phases   were also noticed. The complex morphology of the layers is found to   influence their magnetic properties. Magnetic force microscopy images   revealed an inhomogenous distribution of the magnetic force gradient on   the surface and the formation of magnetic domains in the samples. X-ray   absorption studies of the chemical bonding and local atomic structure   around Mn atoms confirmed high structural and chemical disorder in the   samples. The chemical bonding of the dominating fraction of Mn atoms is   found, however, similar to that in the reference MnSb powder. The x-ray   magnetic circular dichroism measurements reveal an enhanced orbital   moment and a reduced spin moment, which is most likely caused by the   presence of different phases and a Mn-rich surface in the investigated   samples.

  • 268. Lebegue, S
    et al.
    Eriksson, O
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Electronic structure of two-dimensional crystals from ab initio theory2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 11, s. 115409-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on ab initio calculations of the two-dimensional systems MoS2 and NbSe2, which recently were synthesized. We find that two-dimensional MoS2 is a semiconductor with a gap which is rather close to that of the three-dimensional analog, and that NbSe2 is a metal, which is similar to the three-dimensional analog of this compound. We further computed the electronic structure of the two-dimensional hexagonal (graphene-like) lattices of Si and Ge and compared them with the electronic structure of graphene. It is found that the properties related to the Dirac cone do not appear in the case of two-dimensional hexagonal germanium, which is metallic, contrary to two-dimensional hexagonal silicon, also known as silicene, which has an electronic structure very similar to the one of graphene, making them possibly equivalent.

  • 269. Lebegue, S
    et al.
    Klintenberg, Mattias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Katsnelson, M.I.
    Accurate electronic band gap of pure and functionalized graphane from GW calculations2009Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 24, s. 245117-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using the GW approximation, we study the electronic structure of the recently synthesized hydrogenated graphene, named graphane. For both conformations, the minimum band gap is found to be direct at the Gamma point, and it has a value of 5.4 eV in the stable chair conformation, where H atoms attach C atoms alternatively on opposite sides of the two-dimensional carbon network. In the metastable boat conformation the energy gap is 4.9 eV. Then, using a supercell approach, the electronic structure of graphane was modified by introducing either a hydroxyl group or an H vacancy. In this last case, an impurity state appears at about 2 eV above the valence-band maximum.

  • 270.
    Legut, D.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Rusz, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Magnetic exchange interactions and estimation of T-N in CsNiF3 from first principles2008Inngår i: Acta Physica Polonica. A, ISSN 0587-4246, E-ISSN 1898-794X, Vol. 113, nr 1, s. 503-506Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The CsNiF3 has been for long time studied as a prototype of quasi-1D planar ferromagnetic system. At very low temperature the studied system is insulator and therefore the magnetic exchange interactions should decay very rapidly. We treated the magnetic exchange coupling within the Heisenberg model for the nearest neighbor interaction between the antiferromagnetically coupled Ni-chains. The influence of up to the second-nearest neighbors on the ferromagnetic exchange coupling along the Ni-chains was determined. The exchange interactions were calculated for the experimental volume by the density functional theory, within the all-electron approach using the local density approximation for the exchange and correlation. The Neel temperature was calculated by means of the mean-field theory and by the random-phase approximation method.

  • 271.
    Lewin, Erik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Gorgoi, Mihaela
    Schäfers, Franz
    Svensson, Svante
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Jansson, Ulf
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för materialkemi, Oorganisk kemi.
    Influence of sputter damage on the XPS analysis of metastable nanocomposite coatings2009Inngår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 204, nr 4, s. 455-462Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) is a standard method of determining chemical bonding in e.g. nanocomposites. We demonstrate that sputter-cleaning of the sample prior to analysis can substantially alter the attained information. We present an in-depth analysis of sputter damage on binary and ternary TiC-based coatings in the Ti–Ni–C system. XPS was performed after sputter etching with different ion energies (0.15–4 keV). Results are compared to data from the bulk of undamaged samples attained using high kinetic energy XPS. We observe substantial sputter damage, strongly dependent on sputter energies and coating stability. Metastable samples exhibit severe sputter damage after etching with 4 keV. Additional samples from other Ti–Me–C (Me = Al, Fe, Cu or Pt) systems were also examined, and notable sputter damage was observed. This suggests that accurate analysis of any metastable nanocomposite requires careful consideration of sputter damages.

  • 272.
    Li, Sa
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Jena, Puru
    Araújo, C. Moysés
    Ahuja, Rajeev
    Electronic structure and hydrogen desorption in NaAlH42005Inngår i: Mater. Res. Soc. Symp. Proc. (MRS), Vol. 837, nr N2.5.1Artikkel i tidsskrift (Fagfellevurdert)
  • 273.
    Lidbaum, Hans
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik.
    Raanaei, Hossein
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Papaioannou, Evangelos
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Leifer, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Structural and magnetic properties of Co68Fe24Zr8/Al2O3 multilayers2010Inngår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 312, nr 4, s. 580-586Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structural and magnetic properties of Co68Fe24Zr8/Al2O3 multilayers grown by using magnetron Sputtering were investigated with X-ray reflectivity, transmission electron microscopy and magnetooptical Kerr effect. The Co68Fe24Zr8 form amorphous islands when the nominal thickness of the Co68Fe24Zr8 layers is 10 angstrom, exhibiting an isotropic superparamagnetic behavior. Continuous layers with mostly a nano-crystalline structure are instead formed when the nominal thickness of the Co68Fe24Zr8 layers is increased to 20 angstrom. The continuous layers exhibit random, in-plane, magnetic anisotropy resulting from the growth Process. However, induced uniaxial anisotropy is obtained when growing the sample in the presence of an applied magnetic field, regardless of the combination of amorphous and nano-crystalline material.

  • 274.
    Lidbaum, Hans
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik.
    Rusz, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Liebig, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Björgvin, Hjörvarsson
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialfysik.
    Oppeneer, Peter
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Coronel, Ernesto
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Materialteori.
    Leifer, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik.
    Quantitative magnetic information from reciprocal space maps in transmission electron microscopy2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, nr 3, s. 037201-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the most challenging issues in the characterization of magnetic materials is to obtain a quantitative analysis on the nanometer scale. Here we describe how electron magnetic circular dichroism (EMCD) measurements using the transmission electron microscope can be used for that purpose, utilizing reciprocal space maps. Applying the EMCD sum rules, an orbital to spin moment ratio of mL/mS=0.08±0.01 is obtained for Fe, which is consistent with the commonly accepted value. Hence, we establish EMCD as a quantitative element-specific technique for magnetic studies, using a widely available instrument with superior spatial resolution.

  • 275.
    Lidbaum, Hans
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik.
    Rusz, Ján
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Materialteori.
    Rubino, Stefano
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Liebig, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Oppeneer, Peter M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Eriksson, Olle
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Leifer, Klaus
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Experimentell fysik. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Reciprocal and real space maps for EMCD experiments2010Inngår i: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 110, nr 11, s. 1380-1389Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron magnetic chiral dichroism (EMCD) is an emerging tool for quantitative measurements of magnetic properties using the transmission electron microscope (TEM), with the possibility of nanometer resolution. The geometrical conditions, data treatment and electron gun settings are found to influence the EMCD signal. In this article, particular care is taken to obtain a reliable quantitative measurement of the ratio of orbital to spin magnetic moment using energy filtered diffraction patterns. For this purpose, we describe a method for data treatment, normalization and selection of mirror axis. The experimental results are supported by theoretical simulations based on dynamical diffraction and density functional theory. Special settings of the electron gun, so called telefocus mode, enable a higher intensity of the electron beam, as well as a reduction of the influence from artifacts on the signal. Using these settings, we demonstrate the principle of acquiring real space maps of the EMCD signal. This enables advanced characterization of magnetic materials with superior spatial resolution.

  • 276.
    Liebig, Andreas
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Andersson, Gabriella
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Birch, J.
    Hjörvarsson, Björgvin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Stability limits of superlattice growth: the case of Cr/V (001)2008Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, nr 23, s. 8468-8472Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The crystalline quality of bct Cr/V (001) superlattices is found to be strongly dependent on the thickness ratio of the constituents. The out-of-plane coherence length varies from 275 Å to 880 Å, corresponding to 30% and close to 100% of the total film thicknesses, which was kept the same for all the samples. The width of the rocking curve (mosaicity) varies as much as from below 0.02° to 0.8°. Using an adaptation of the Matthews–Blakeslee theory for critical thickness, we define a parameter window available for the growth of superior Cr/V (001) superlattices.

  • 277.
    Lindblad, A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Bergersen, H.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Pokapanich, W.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Tchaplyguine, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Öhrwall, G.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Björneholm, O.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Charge delocalization dynamics of ammonia in different hydrogen bonding environments: free clusters and in liquid water solution2009Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, nr 11, s. 1758-1764Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Valence and core level photoelectron spectra and Auger electron spectra of ammonia in pure clusters have been measured. The Auger electro  spectra of gas-phase ammonia, pure ammonia clusters and ammonia in   aqueous solution are compared and interpreted via ab initio calculations of the Auger spectrum of the ammonia monomer and dimer. The calculations reveal that the final two-hole valence states can be   delocalized over both ammonia molecules. Features at energies   pertaining to delocalized states involving one, or more, hydroge  bonding orbitals can be found in both the ammonia cluster Auger   electron spectrum and in that of the liquid solvated molecule. The lower Coulombic repulsion between two delocalized valence final state holes gives higher kinetic energy of the Auger electrons which is also   observed in the spectra. This decay path-specific to the condensed   phase-is responsible for more than 5% of the total cluster Auger intensity. Moreover, this interpretation is also applicable to the   solid phase since the same features have been observed, but not assigned, in the Auger spectrum of solid ammonia.

  • 278.
    Lindblad, A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Bergersen, H.
    Rander, T.
    Lundwall, M.
    Öhrwall, G.
    Tchaplyguine, M.
    Svensson, S.
    Björneholm, O.
    The far from equilibrium structure of argon clusters doped with krypton or xenon.2006Inngår i: Physical Chemistry Chemical Physics, Vol. 8, nr 16, s. 1899-1905Artikkel i tidsskrift (Fagfellevurdert)
  • 279.
    Lindblad, A.
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    Fink, R. F. F.
    Björneholm, O.
    Bergersen, H.
    Lundwall, M.
    Rander, T.
    Feifel, R.
    Öhrwall, G.
    Tchaplyguine, M.
    Hergenhahn, U.
    Svensson, S.
    Postcollision interaction in noble gas clusters: observation of differences in surface and bulk line shapes2005Inngår i: The Journal of Chemical Physics, ISSN 0021-9606, Vol. 123, nr 21, s. 211101-4Artikkel i tidsskrift (Fagfellevurdert)
  • 280.
    Lindblad, A
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Winkler, M.
    Tchaplyguine, M.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Öhrwall, G.
    Svensson, S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    Björneholm, O.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap, Yt- och gränsskiktsvetenskap.
    The geometric structure of pure SF6 and mixed Ar/SF6 clusters investigated by core level photoelectron spectroscopy2009Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, nr 3, s. 433-436Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The S 2p core level photoelectron spectra of Sulphurhexafluoride   Clusters have been investigated together with heterogeneous Ar/SF6 clusters, created by doping Ar host clusters (with a mean size of 3600   atoms) with the molecule. Surface and bulk features are resolved both   in the argon 2p and the sulphur 2p core level photoelectron spectra.  For the latter level such features were only observed in the pure   cluster case; a single feature characterizes the S 2p core level  spectra of SF6 doped argon clusters. From the chemical shifts,  investigated with respect to SF6 doping pressure. It can be concluded   that the host clusters get smaller with increasing doping pressures and  that the SF6 molecules predominantly stay below the cluster surface,   whereas the Argon core stays intact. We have neither observed features   corresponding to SF6 on the cluster Surface, nor features corresponding   to molecules deep inside the bulk in any of the spectra from the pick-up experiments.

  • 281.
    Lindblad, Andreas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och materialvetenskap.
    A Treatise on the Geometric and Electronic Structure of Clusters: Investigated by Synchrotron Radiation Based Electron Spectroscopies2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Clusters are finite ensembles of atoms or molecules with sizes in the nanometer regime (i.e. nanoparticles). This thesis present results on the geometric and electronic structure of homogeneous and heterogeneous combinations of atoms and molecules. The systems have been studied with synchrotron radiation and valence, core and Auger electron spectroscopic techniques.

    The first theme of the thesis is that of mixed clusters. It is shown that by varying the cluster production technique both structures that are close to that predicted by equilibrium considerations can be attained as well as far from equilibrium structures.

    Electronic processes following ionization constitute the second theme. The post-collision interaction phenomenon, energy exchange between the photo- and the Auger electrons, is shown to be different in clusters of argon, krypton and xenon. A model is proposed that takes polarization screening in the final state into account. This result is of general character and should be applicable to the analysis of core level photoelectron and Auger electron spectra of insulating and semi-conducting bulk materials as well.

    Interatomic Coloumbic Decay is a process that can occur in the condensed phases of weakly bonded systems. Results on the time-scale of the process in Ne clusters and mixed Ar/Ne clusters are herein discussed, as well observations of resonant contributions to the process. In analogy to Auger vis-à-vis Resonant Auger it is found that to the ICD process there is a corresponding Resonant ICD process possible. This has later been observed in other systems and by theoretical calculations as well in subsequent works by other groups.

    Delocalization of dicationic valence final states in the hydrogen bonded ammonia clusters and aqueous ammonia has also been investigated by Auger electron spectroscopy. With those results it was possible to assign a previously observed feature in the Auger electron spectrum of solid ammonia.

    Delarbeid
    1. Postcollision interaction in noble gas clusters: observation of differences in surface and bulk line shapes
    Åpne denne publikasjonen i ny fane eller vindu >>Postcollision interaction in noble gas clusters: observation of differences in surface and bulk line shapes
    Vise andre…
    2005 Inngår i: The Journal of Chemical Physics, ISSN 0021-9606, Vol. 123, nr 21, s. 211101-4Artikkel i tidsskrift (Fagfellevurdert) Published
    Identifikatorer
    urn:nbn:se:uu:diva-96747 (URN)
    Tilgjengelig fra: 2008-02-28 Laget: 2008-02-28bibliografisk kontrollert
    2. Radial surface segregation in free heterogeneous argon/krypton clusters
    Åpne denne publikasjonen i ny fane eller vindu >>Radial surface segregation in free heterogeneous argon/krypton clusters
    Vise andre…
    2004 Inngår i: Chemical Physics Letters, Vol. 392, nr 4-6, s. 433-438Artikkel i tidsskrift (Fagfellevurdert) Published
    Identifikatorer
    urn:nbn:se:uu:diva-96748 (URN)
    Tilgjengelig fra: 2008-02-28 Laget: 2008-02-28bibliografisk kontrollert
    3. Chemical shifts of small heterogeneous Ar/Xe clusters
    Åpne denne publikasjonen i ny fane eller vindu >>Chemical shifts of small heterogeneous Ar/Xe clusters
    Vise andre…
    2011 (engelsk)Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, nr 12, s. 125414-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Heterogeneous rare-gas clusters produced by a coexpansion of an argon/xenon mixture have been studied using synchrotron-radiation-based photoelectron spectroscopy. Both valence and Xe 4d(5/2) core-level photoelectron spectra were recorded for three different concentrations of the primary argon/xenon mixture and, for those mixtures, spectra were recorded at several different stagnation conditions. The studied size regime of the mixed clusters ranges from large, similar to those studied in an earlier paper [Phys. Rev. A 69, 031210(R) (2004)], to very small-as reflected in the cluster line shapes and chemical shifts. The chemical shifts obtained from a curve fitting procedure similar to that used in our earlier paper are discussed in terms of the mixed cluster structure which can be expected from equilibrium considerations and the Lennard-Jones parameters of the constituent atoms. Molecular dynamics simulations of the vertical polarization shifts allow more specific assignments of "on-top" sites and interfacial sites.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-96749 (URN)10.1103/PhysRevB.83.125414 (DOI)000288646500007 ()
    Tilgjengelig fra: 2008-02-28 Laget: 2008-02-28 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    4. Self-assembled heterogeneous argon/neon core-shell clusters studied by photoelectron spectroscopy
    Åpne denne publikasjonen i ny fane eller vindu >>Self-assembled heterogeneous argon/neon core-shell clusters studied by photoelectron spectroscopy
    Vise andre…
    2007 (engelsk)Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 126, nr 21, s. 214706-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Clusters formed by a coexpansion process of argon and neon have been studied using synchrotron radiation. Electrons from interatomic Coulombic decay as well as ultraviolet and x-ray photoelectron spectroscopy were used to determine the heterogeneous nature of the clusters and the cluster structure. Binary clusters of argon and neon produced by coexpansion are shown to exhibit a core-shell structure placing argon in the core and neon in the outer shells. Furthermore, the authors show that 2 ML of neon on the argon core is sufficient for neon valence band formation resembling the neon solid. For 1 ML of neon the authors observe a bandwidth narrowing to about half of the bulk value.

    Emneord
    Spectroscopy and geometrical structure of clusters, Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals, Photoemission and photoelectron spectra
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-96750 (URN)10.1063/1.2735607 (DOI)000247106600033 ()
    Tilgjengelig fra: 2008-02-28 Laget: 2008-02-28 Sist oppdatert: 2017-12-14
    5. The geometric structure of pure SF6 and mixed Ar/SF6 clusters investigated by core level photoelectron spectroscopy
    Åpne denne publikasjonen i ny fane eller vindu >>The geometric structure of pure SF6 and mixed Ar/SF6 clusters investigated by core level photoelectron spectroscopy