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  • 3551. Tacchi, S.
    et al.
    Grånäs, Oscar
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stollo, A.
    Madami, M.
    Gubbiotti, G.
    Carlotti, G.
    Marangolo, M.
    Eddrief, M.
    Etgens, V. H.
    Yadav, M. K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nordström, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sanyal, Biplab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Epitaxial Fe films on ZnSe(001): effect of the substrate surface reconstruction on the magnetic anisotropy2012In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 23, p. 236006-Article in journal (Refereed)
    Abstract [en]

    It is well known that Fe films deposited on a c(2 x 2)-reconstructed ZnSe(001) surface show a strong in-plane uniaxial magnetic anisotropy. Here, the effect of the substrate reconstruction on the magnetic anisotropy of Fe has been studied by in situ Brillouin light scattering. We found that the in-plane uniaxial anisotropy is strongly reduced for Fe films grown on a (1 x 1)-unreconstructed ZnSe substrate while the in-plane biaxial one is nearly unaffected by the substrate reconstruction. Calculations of magnetic anisotropy energies within the framework of ab initio density functional theory reveal that the strong suppression of anisotropy at the (1 x 1) interface occurs due to complex atomic relaxations as well as the competing effects originating from magnetocrystalline anisotropy and dipole-dipole interactions. For both sharp and intermixed c(2 x 2) interfaces, the magnetic anisotropy is enhanced compared to the (1 x 1) case due to the further lowering of symmetry. The theoretical results are in agreement with the experimental findings. 

  • 3552.
    Tagliati, Stella
    Stockholm University, Faculty of Science, Department of Physics.
    Membrane-based nanocalorimetry for low temperature studies with high resolution and absolute accuracy2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A differential, membrane-based nanocalorimeter has been designed and constructed for thermal studies of mesoscopic samples at low temperatures. The calorimeter is intended for sample masses from mg to sub-μg and a broad temperature range from above room temperature down to the sub-K region. It allows concurrent use of ac steady state and relaxation methods. Effort was spent to achieve good absolute accuracy to enable investigations of the electronic contribution to the heat capacity of superconductors. The calorimeter consists of a pair of cells, each of which is a stack of heaters and thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The device has several distinctive features: i) The resistive thermometer, made of a GeAu alloy, displays a high sensitivity, dlnR/dlnT ≈ −1 over the entire temperature range. ii) The sample is placed in direct contact with the thermometer, which is allowed to self-heat. The thermometer can thus be operated at high dc current to increase the resolution. iii) Data are acquired with a set of eight synchronized lock-in amplifiers measuring dc, 1st and 2nd harmonic signals of heaters and thermometer. iv) Absolute accuracy is achieved via a novel variable-frequency fixed-phase technique in which the measurement frequency is automatically adjusted during ac-calorimetry measurements to account for the temperature variation of the sample specific heat and the device thermal conductance. The properties of the empty cell and the effect of the thermal link between sample and cell were analytically studied. Practical expressions for describing the frequency dependence of heat capacity, thermal conductance, and temperature oscillation amplitude of the system were formulated. Comparisons with measurements and numerical simulations show excellent agreement. Calibration procedures are simple, but care should be taken to minimize thermal radiation effects. The experimental setup is operated with self-regulation of heater powers and thermometer bias, including compensation to zero the differential dc signal. As a result its high resolution and compact format, the calorimeter is well suited for studies of phase transitions and phase diagrams as well as electronic specific heat. The performance of the device is demonstrated by a study of the superconducting state of a small lead crystal.

  • 3553.
    Tagliati, Stella
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Absolute accuracy in membrane-based ac nanocalorimetry2011In: Thermochimica Acta, ISSN 0040-6031, E-ISSN 1872-762X, Vol. 522, no 1-2, p. 66-71Article in journal (Refereed)
    Abstract [en]

    To achieve accurate results in nanocalorimetry a detailed analysis and understanding of the behavior of the calorimetric system is required. There are especially two system-related aspects that should be taken in consideration: the properties of the empty cell and the effect of the thermal link between sample and cell. Here we study these two aspects for a membrane-based system where heater and thermometer are both in good contact with each other and the center of the membrane. Practical, analytical expressions for describing the frequency dependence of heat capacity, thermal conductance, and temperature oscillation of the system are formulated and compared with measurements and numerical simulations. We finally discuss the experimental conditions for an optimal working frequency, where high resolution and good absolute accuracy are combined.

  • 3554.
    Tagliati, Stella
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Absolute specific heat measurements of a microgram Pb crystal using ac nanocalorimetry2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 400, no 022120Article in journal (Refereed)
    Abstract [en]

    Heat capacity measurements using the ac steady state method are often considered difficult to provide absolute accuracy. By adjusting the working frequency to maintain a constant phase and using the phase information to obtain the heat capacity, we have found that it is possible to achieve good absolute accuracy. Here we present a thermodynamic study of a ~2.6 μg Pb superconducting crystal to demonstrate the newly opened capabilities. The sample is measured using a differential membrane-based calorimeter. The custom-made calorimetric cell is a pile of thin film Ti heater, insulation layer and Ge1-xAux thermometer fabricated in the center of two Si3N4 membranes. It has a background heat capacity < 100 nJ/K at 300 K, decreasing to 9 pJ/K at 1 K. The sample is characterized at temperatures down to 0.5 K. The zero field transition at Tc = 7.21 K has a width ≈20 mK and displays no upturn in C. From the heat capacity jump at Tc and the extrapolated Sommerfeld term we find ΔC/γTc = 2.68. The latent heat curve obtained from the zero field heat capacity measurement, and the deviations of the thermodynamic critical field from the empirical expression Hc = Hc(0)[1-(T/Tc)2] are discussed. Both analyses give results in good agreement with literature.

  • 3555.
    Tagliati, Stella
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Rydh, Andreas
    Stockholm University, Faculty of Science, Department of Physics.
    Xie, R.
    Argonne National Laboratory, USA.
    Welp, U.
    Argonne National Laboratory, USA.
    Kwok, W. K.
    Argonne National Laboratory, USA.
    Membrane-based calorimetry for studies of sub-microgram samples2009In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 150, p. 052256-Article in journal (Refereed)
    Abstract [en]

    We have developed a membrane-based microcalorimeter for general measurements of heat capacity and latent heat using a combination of ac steady-state and relaxation methods. The differential calorimeter is designed for sub-microgram samples studied over a wide range of temperatures and magnetic fields. The device is based on free-standing silicon nitride membranes of 150 nm thickness onto which thin film heaters and temperature sensors are fabricated. While production-line fabrication may benefit from back-etching as a final step, it is often easier to start with pre-etched membranes in a research laboratory. With selected nano-fabrication methods this is possible. Due to a robust heater and very low thermal conductance of the final calorimeter, the sample can be heated to more than 100 K above base temperature. This enables instantaneous calibration, and makes the device capable of being used for ultra-fast temperature control, relaxation studies, and measurements that combine good absolute accuracy, high resolution, and information on latent heat.

  • 3556.
    Tal, Alexey
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Katsnelson, Mikhail I.
    Radboud University of Nijmegen, Netherlands; Ural Federal University, Russia.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Dubrovinsky, Leonid
    University of Bayreuth, Germany.
    Dubrovinskaia, Natalia
    University of Bayreuth, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National University of Science and Technology MISIS, Russia.
    Pressure-induced crossing of the core levels in 5d metals2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 93, no 20, p. 205150-Article in journal (Refereed)
    Abstract [en]

    A pressure-induced interaction between core electrons, the core-level crossing (CLC) transition, has been observed in hcp Os at P approximate to 400 GPa [L. Dubrovinsky et al., Nature (London) 525, 226 (2015)]. By carrying out a systematic theoretical study for all metals of the 5d series (Hf, Ta, W, Re, Os, Ir, Pt, Au) we have found that the CLC transition is a general effect for this series of metals. While in Pt it occurs at approximate to 1500 GPa, at a pressure substantially higher than in Os, in Ir it occurs already at 80 GPa. Moreover, we predict that in Re the CLC transition may take place already at ambient pressure. We explain the effect of the CLC and analyze the shift of the transition pressure across the series within the Thomas-Fermi model. In particular, we show that the effect has many common features with the atomic collapse in rare-earth elements.

  • 3557.
    Talyzin, Alexander V.
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Yu. O.
    Schaub, T.M.
    Mauron, P.
    Shulga, Yu.M.
    Züttel, Andreas
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Marshall, A.G.
    Composition of hydrofullerene mixtures produced by C60 reaction with hydrogen gas revealed by high-resolution mass spectrometry.2005In: Journal of Physical Chemistry B, ISSN 1520-6106, Vol. 109, no 26, p. 12742-12747Article in journal (Refereed)
    Abstract [en]

    Complex solid hydrofulleride mixtures were synthesized by prolonged hydrogenation of C60 at 120 bar hydrogen pressure, 673 K temperature, and different reaction periods. The high degree of hydrogenation was confirmed by infrared spectroscopy and X-ray diffraction. The identity of hydrogenation products was determined by high-resolution field desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry. Despite partial gas-phase fragmentation of hydrofullerene ions during mass analysis, the data suggest that the synthesized mixtures consist of mostly C58-60Hx hydrofullerenes. Increasing the duration of hydrogenation results in synthesis of C59Hx and C58Hx as major products. Possible hydrofullerene fragmentation pathways during both material synthesis and mass spectrometric analysis are discussed. Gas-phase fragmentation in the mass spectrometer arises from hydrofullerene ions C60Hx+ with x > 40 and C59H44+ with drastically decreased molecular stability relative to the known C60H36.

  • 3558.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Feasibility of H2–THF–H2O clathrate hydrates for hydrogen storage applications2008In: International Journal of Hydrogen Energy, Vol. 33, no 1, p. 111-115Article in journal (Refereed)
    Abstract [sv]

    Hydrogen storage capacity of hydrogen clathrate hydrates H2–THF–H2O was directly measured using gravimetric method. The amount of hydrogen stored in a bulk piece of ice was below even after prolonged exposure to hydrogen at . It is confirmed that fine dispersion of material is required to improve kinetics of hydrogen uptake. To achieve a fine dispersion of ice grains, it is proposed to use rather common light framework materials with size of pore sizes of about as a support media. The samples dispersed in foamed polyurethane showed measurable hydrogen uptake at pressure and release. However, the amount of stored hydrogen was found maximum on the level of .

  • 3559.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Kurnosov, Alexander
    Dubrovinsky, Leonid
    High pressure phase transition in LiBH42007In: Journal of Solid State Chemistry, ISSN 0022-4596, Vol. 180, no 2, p. 510-7Article in journal (Refereed)
    Abstract [en]

    The high-pressure phase transition from ambient pressure alpha-LiBH4 to high-pressure beta-LiBH4 was observed by Raman spectroscopy and X-ray diffraction between 0.8 and 1.1 GPa. The phase boundary between these two phases was mapped over a large range of temperatures using thermal conductivity studies and differential thermal analysis. The structure of the high-pressure phase could not be identified due to small number of experimentally observed reflections, but it was shown that it is different from previously reported theoretical predictions.

  • 3560.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Dzwilewski, Andrzej
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Y.
    Purcell, J.M.
    Marshall, A.G.
    Shulga, Y.
    McCammon, C.
    Dubrovinsky, Leonid
    Hydrogenation of C60 at 2 GPa Pressure and High Temperature.2006In: Chemical Physics, ISSN 0301-0104, Vol. 325, no 2-3, p. 445-451Article in journal (Refereed)
    Abstract [en]

    Hydrogenation of C60 at 2 GPa and 723–823 K was performed with thermal decomposition of LiAlH4 as a hydrogen source. Analysis

    of hydrogenation products showed that the method can produce not only C60H36, but also hydrofullerides C60Hx with 44 < x < 52.

    Unlike other hydrogenation methods in which pristine C60 reacts with hydrogen, the high pressure/high temperature conditions result

    first in C60 polymerization into a tetragonal phase which later reacts with hydrogen. It is suggested that hydrogen first attacks intermolecular

    carbon–carbon bonds, resulting in complete depolymerization of C60 at a later stage of the hydrogenation process. This model

    suggests the possibility to select starting points for hydrogenation by choosing specific polymeric structures of C60. Hydrogenated polymeric

    C60 was identified as an intermediate reaction product. Characterization of highly reduced material was performed by Raman and

    IR spectroscopy, X-ray diffraction, and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass

    spectrometry.

  • 3561.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hausmaninger, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    You, Shujie
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Szabo, Tamas
    Department of Physical Chemistry and Materials Science, University of Szeged, Szeged, Hungary.
    The structure of graphene oxide membranes in liquid water, ethanol and water – ethanol mixtures2014In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, p. 272-281Article in journal (Refereed)
    Abstract [en]

    The structure of graphene oxide (GO) membranes was studied in situ in liquid solvents using synchrotron radiation X-ray diffraction in a broad temperature interval. GO membranes are hydrated by water similarly to precursor graphite oxide powders but intercalation of alcohols is strongly hindered, which explains why the GO membranes are permeated by water and not by ethanol. Insertion of ethanol into the membrane structure is limited to only one monolayer in the whole studied temperature range, in contrast to precursor graphite oxide powders, which are intercalated with up to two ethanol monolayers (Brodie) and four ethanol monolayers (Hummers). As a result, GO membranes demonstrate the absence of “negative thermal expansion” and phase transitions connected to insertion/de-insertion of alcohols upon temperature variations reported earlier for graphite oxide powders. Therefore, GO membranes are a distinct type of material with unique solvation properties compared to parent graphite oxides even if they are composed of the same graphene oxide flakes.

  • 3562.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Luzan, Serhiy
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Pressure-induced insertion of liquid acetone into the graphite oxide structure2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 11, p. 7004-7006Article in journal (Refereed)
    Abstract [en]

    An expansion of the graphite oxide structure due to pressure-induced insertion of acetone solvent was observed upon compression at 0.9 GPa. However, conversion into the expanded high-pressure phase is not complete, with the high-pressure and the ambient-pressure phases coexisting even at pressures up to 4.5 GPa. The phase transformation is not correlated with the solidification point of acetone, a behavior similar to that of the graphite oxide/alcohol systems and unlike that of the previously studied graphite oxide/water system. It can be concluded that pressure-induced insertion of solvent into the graphite oxide structure occurs not only for protic solvents (water, methanol, ethanol) but also for aprotic polar solvents (acetone).

  • 3563.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Luzan, Serhiy
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Temperature dependent structural breathing of hydrated graphite oxide in H2O  2011In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, no 6, p. 1894-1899Article in journal (Refereed)
    Abstract [en]

    Hydration of graphite oxide by excess of water was studied in the temperature interval 295–230 K. A structural breathing effect is found for fully hydrated graphite oxide near the water solidification/melting point. Expansion of hydrated graphite oxide structure due to insertion of additional water occurs upon cooling down from ambient temperature to the point of water media freezing. Cooling down below the point of water medium solidification results in stepwise contraction of graphite oxide interlayer distance by 25% due to partial withdrawal of water from the hydrated structure. Heating back from 230 K to ambient temperature results in graphite oxide structure expansion due absorption of water from medium, thus making a reversible cycle. The effect of structure breathing is important for any chemical treatments performed with graphite oxide in solution, e.g. graphite oxide functionalization and conversion into graphene-related materials.

  • 3564.
    Talyzin, Alexandr
    et al.
    Department of Physics, Umeå University.
    Luzan, S.M.
    Department of Physics, Umeå University.
    Leifer, Klaus
    Division for Electron Microscopy and Nanoengineering, Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, Box 534, SE-75121 Uppsala, Sweden.
    Akhtar, S.
    Division for Electron Microscopy and Nanoengineering, Department of Engineering Sciences, The Ångström Laboratory, Uppsala University, Box 534, SE-75121 Uppsala, Sweden.
    Fetzer, J
    Fetzpahs Consulting, P.O. Box 942, Pinole, California 94564, United States.
    Cataldo, F
    Istituto Nazionale di Astrofisica .
    Tsybin, Y.O.
    Biomolecular Mass Spectrometry Laboratory, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne, Switzerland.
    Tai, C.W.
    Department of Materials and Environmental Chemistry, Stockholm University, S-106 91 Stockholm, Sweden.
    Dzwilewski, Andrzej
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering.
    Moons, Ellen
    Karlstad University, Faculty of Technology and Science, Department of Physics and Electrical Engineering. Karlstad University, Faculty of Technology and Science, Materials Science.
    Coronene fusion by heat treatment: Road to nanographenes2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 27, p. 13207-13214Article in journal (Refereed)
    Abstract [en]

    The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500700 C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530-550 C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550600 C by oligomerization into larger molecules. Above 600 C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.

  • 3565.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Mercier, Guillaume
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Klechikov, Alexey
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hedenström, Mattias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Johnels, Dan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Wei, Di
    Cotton, Darryl
    Opitz, Andreas
    Moons, Ellen
    Brodie vs Hummers graphite oxides for preparation of multi-layered materials2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 115, p. 430-440Article in journal (Refereed)
    Abstract [en]

    Graphite oxides synthesized by one and two step Brodie oxidation (BGO) and Hummers (HGO) methods were analyzed by a variety of characterization methods in order to evaluate the reasons behind the difference in their properties. It is found that the Brodie method results in a higher relative amount of hydroxyl groups and a more homogeneous overall distribution of functional groups over the planar surface of the graphene oxide flakes. The higher number of carbonyl and carboxyl groups in HGO, detected by several methods, including XPS, NMR and FTIR, unavoidably results in defects of the graphene "skeleton", holes and overall disruption of the carbon-carbon bond network, stronger deviation from planar flake shape and poor ordering of the graphene oxide layers. It is also suggested that functional groups in HGO are less homogeneously distributed over the flake surface, forming some nanometer-sized graphene areas. The presence of differently oxidized areas on the GO surface results in inhomogeneous solvation and hydration of HGO and effects of inter- and intra-stratification. The proposed interpretation of the data explains the higher mechanical strength of multi-layered BGO membranes/papers, which are also less affected by humidity changes, thus providing an example of a membrane property superior to that of HGO.

  • 3566.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Solozhenko, Vladimir L.
    Kurakevych, Oleksandr O.
    Szabó, Tamás
    Dékány, Imre
    Kurnosov, Alexandr
    Dmitriev, Vladimir
    Colossal Pressure-Induced Lattice Expansion of Graphite Oxide in the Presence of Water2008In: Angewandte Chemie International Edition, Vol. 47, no 43, p. 8268-8271Article in journal (Refereed)
  • 3567.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    High pressure study of NaAlH4 by Raman spectroscopy up to 17 GPa2006In: High Pressure Research, ISSN 0895-7959, Vol. 26, no 3, p. 165-73Article in journal (Refereed)
    Abstract [en]

    A high-pressure Raman study was carried out on NaA1H(4) up to 17 GPa using the diamond anvil cell method. In the pressure region 2-5 GPa, several of the original modes split. Although this might be a sign of some structural change, the spectral changes do not allow us to claim the existence of a clear phase transition in this pressure range. The spectra revert to their ambient pressure forms on decreasing pressure below < 3.0-1.4 GPa. A phase transition to beta-NaA1H(4) was found at 14-16 GPa. This phase transition is also reversible with an unusually strong hysteresis: the beta-NaA1H(4) can be followed upon decompression down to 3.9 GPa. Analysis of Raman data shows that this phase transition is compatible with a theoretical prediction of a strong volume collapse.

  • 3568.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Reversible phase transition in LiAlH4 under high pressure conditions.2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 18, p. 180101(R)-Article in journal (Refereed)
    Abstract [en]

    The structural stability of the hydrogen storage compound LiAlH4 was studied by Raman spectroscopy in the pressure interval 0–6 GPa. A slow phase transition from a-LiAlH4 to a b phase was observed to occur between 2.2 and 3.5 GPa. The phase transition is reversible and a reverse transformation to a-LiAlH4 was observed below 1.4 GPa. Analysis of Raman spectra from b-LiAlH4 shows that they cannot be explained by the theoretically predicted a-NaAlH4-type structure with I41 /a symmetry.

  • 3569.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Araujo, C. Moysés
    Ahuja, Rajeev
    Raman spectroscopy and structural transformations in hydrides under pressure.2005In: Proceedings of the Joint 20th AIRAPT and 43rd EHPRG Conf. on High Pressure Science and Technology, Karlsruhe 2005, 2005, p. T5-P027Conference paper (Other academic)
    Abstract [en]

    We have investigated the structural stability of the hydrides LiAlH4, NaAlH4, and NaBH4 under high pressure at room temperature using Raman spectroscopy. For all compounds studied we observe reversible structural phase transformations under pressure. The Raman results are not always compatible with the structures predicted by earlier theoretical calculations for the high-pressure phases, and further theoretical studies of the stability of NaBH4 under pressure have been carried out.

  • 3570.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Yu. O.
    Purcell, J.M.
    Schaub, T.M.
    Shulga, Yu.M.
    Noreus, Dag
    Sato, T.
    Dzwilewski, Andrzej
    Umeå University, Faculty of Science and Technology, Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Marshall, A.G.
    Reaction of hydrogen gas with C60 at elevated pressure and temperature: Hydrogenation and cage fragmentation.2006In: Journal of Physical Chemistry A, ISSN 1089-5639, Vol. 110, no 27, p. 8528-34Article in journal (Refereed)
    Abstract [en]

    Products of the reaction of C60 with H2 gas have been monitored by high-resolution atmospheric pressure

    photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray

    diffraction, and IR spectroscopy as a function of hydrogenation period. Samples were synthesized at 673 K

    and 120 bar hydrogen pressure for hydrogenation periods between 300 and 5000 min, resulting in the formation

    of hydrofullerene mixtures with hydrogen content ranging from 1.6 to 5.3 wt %. Highly reduced C60Hx (x >

    36-40) and products of their fragmentation were identified in these samples by APPI FT-ICR MS. A sharp

    change in structure was observed for samples with at least 5.0 wt % of hydrogen. Low-mass (300-500 Da)

    hydrogenation products not observed by prior field desorption (FD) FT-ICR MS were detected by APPI

    FT-ICR MS and their elemental compositions obtained for the first time. Synthetic and analytical fragmentation

    pathways are discussed.

  • 3571.
    Talyzin, Alexandr
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Tsybin, Yu.O.
    Peera, A.A.
    Schaub, T.M.
    Marshall, A.G.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Mauron, P.
    Züttel, A.
    Billups, W.E.
    Synthesis of C59Hx and C58Hx fullerenes stabilized by hydrogen2005In: Journal of Physical Chemistry B Letters, ISSN 1520-6106, Vol. 109, no 12, p. 5403-5Article in journal (Refereed)
    Abstract [en]

    Prolonged hydrogenation of C60 molecules by reaction with H2 at elevated temperature and pressure results

    in fragmentation and collapse of the fullerene cage structure. However, fragments can be preserved by

    immediate termination of dangling bonds by hydrogen. Here we demonstrate that not only fullerene fragments

    but also hydrogenated fragmented fullerenes (e.g., C58H40 and C59H40) can be synthesized in bulk amount by

    high-temperature hydrogenation of C60. We confirm successful synthesis of these species by matrix-assisted

    laser desorption ionization time-of-flight mass spectrometry and complete speciation of the resultant complex

    fullerene mixtures by high-resolution field desorption/ionization Fourier transform ion cyclotron resonance

    mass spectrometry.

  • 3572.
    Talyzin, Alexandr V.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Anoshkin, Ilya V.
    Nasibulin, Albert G.
    High-temperature transformations of coronene-based graphene nanoribbons encapsulated in SWNTs2015In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 11, p. 2491-2495Article in journal (Refereed)
    Abstract [en]

    Coronene-based graphene nanoribbons encapsulated inside single-walled carbon nanotubes (SWNTs) were prepared 440 degrees C under Ar and annealed at temperatures up to 825 degrees C. The structural modifications of coronene/SWNT samples were studied using Raman spectroscopy and transmission electron microscopy. Coronene and coronene-based graphene nanoribbons are hydrogen terminated and annealing at temperatures above the stability limit of C-H bonds were expected to result in formation of new products. Indeed, Raman spectroscopy revealed the appearance of new sharp peaks after annealing of samples above 650 degrees C. The possible nature of encapsulated products produced by annealing of hydrogen terminated nanoribbons inside SWNTs is discussed. 

  • 3573.
    Talyzin, Alexandr V.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Szabó, Tamas
    Dmitriev, Vladimir
    Structural breathing of graphite oxide pressurized in basic and acidic solutions2011In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 2, no 4, p. 309-313Article in journal (Refereed)
    Abstract [en]

    Graphite oxide immersed in excess of basic or acidic water media was studied using synchrotron X-ray diffraction at high pressure using diamond anvil cells. The lattice spacing of graphite oxide in excess of NaOH solution increases by the enormous value of 85% at 1.6 GPa. In contrast, structure expansion of graphite oxide immersed in liquid water with added HCl is significantly less pronounced compared with compression in pure water. The point of media solidification correlated with a sharp decrease in graphite oxide layers separation because of partial withdrawal of water from the structure. Therefore, pressure-induced structural breathing of graphite oxide due to insertion/desertion of water into/from interlayer space is strongly enhanced in basic media and suppressed in acidic media. The magnitude of structural breathing also depends on relative amounts of graphite oxide powder and solution. Strongly diluted samples with low relative amount of graphite oxide powder in the suspension exhibited less pronounced high-pressure anomaly.

  • 3574.
    Talyzin, Alexandr V.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Szabó, Tamás
    Dékány, Imre
    Dmitriev, Vladimir
    Pressure-induced insertion of liquid alcohols into graphite oxide structure2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 51, p. 18445-18449Article in journal (Refereed)
    Abstract [en]

    Graphite oxide (GO) immersed in an excess of methanol and ethanol media is found to undergo a phase transformation at about 0.2−0.8 GPa, with an expansion of the unit cell volume by 40%, due to pressure-induced insertion of solvent into interlayer space. The pressure at which the structural expansion occurs does not correlate with the solidification pressure of the alcohol, in contrast to the graphite oxide/water system. The expanded high-pressure phase of GO/ethanol could be quenched back to ambient pressure. Compression of graphite oxide with a 2:1 water/methanol medium revealed a complex anomaly with two steps attributed to insertion of methanol and water at different pressure points.

  • 3575.
    Tamm, A.
    et al.
    Lawrence Livermore Natl Lab, Quantum Simulat Grp, Livermore, CA 94550 USA.
    Caro, M.
    Virginia Polytech Inst & State Univ, Dept Mech Engn, Arlington, VA 22033 USA.
    Caro, A.
    George Washington Univ, Ashburn, VA 20147 USA.
    Samolyuk, G.
    Oak Ridge Natl Lab, Mat Sci & Technol Div, POB 2009, Oak Ridge, TN 37831 USA.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Correa, A. A.
    Lawrence Livermore Natl Lab, Quantum Simulat Grp, Livermore, CA 94550 USA.
    Langevin Dynamics with Spatial Correlations as a Model for Electron-Phonon Coupling2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 120, no 18, article id 185501Article in journal (Refereed)
    Abstract [en]

    Stochastic Langevin dynamics has been traditionally used as a tool to describe nonequilibrium processes. When utilized in systems with collective modes, traditional Langevin dynamics relaxes all modes indiscriminately, regardless of their wavelength. We propose a generalization of Langevin dynamics that can capture a differential coupling between collective modes and the bath, by introducing spatial correlations in the random forces. This allows modeling the electronic subsystem in a metal as a generalized Langevin bath endowed with a concept of locality, greatly improving the capabilities of the two-temperature model. The specific form proposed here for the spatial correlations produces a physical wave-vector and polarization dependency of the relaxation produced by the electron-phonon coupling in a solid. We show that the resulting model can be used for describing the path to equilibration of ions and electrons and also as a thermostat to sample the equilibrium canonical ensemble. By extension, the family of models presented here can be applied in general to any dense system, solids, alloys, and dense plasmas. As an example, we apply the model to study the nonequilibrium dynamics of an electron-ion two-temperature Ni crystal.

  • 3576.
    Tamm, A.
    et al.
    Los Alamos Natl Lab, Div Mat Sci & Technol, Los Alamos, NM 87545 USA.;Univ Tartu, Inst Technol, IMS Lab, EE-50411 Tartu, Estonia..
    Samolyuk, G.
    Oak Ridge Natl Lab, Div Mat Sci & Technol, Oak Ridge, TN USA..
    Correa, A. A.
    Lawrence Livermore Natl Lab, Livermore, CA 94550 USA..
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Aabloo, A.
    Univ Tartu, Inst Technol, IMS Lab, EE-50411 Tartu, Estonia..
    Caro, A.
    Los Alamos Natl Lab, Div Mat Sci & Technol, Los Alamos, NM 87545 USA..
    Electron-phonon interaction within classical molecular dynamics2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 2, article id 024305Article in journal (Refereed)
    Abstract [en]

    We present a model for nonadiabatic classical molecular dynamics simulations that captures with high accuracy the wave-vector q dependence of the phonon lifetimes, in agreement with quantum mechanics calculations. It is based on a local view of the e-ph interaction where individual atom dynamics couples to electrons via a damping term that is obtained as the low-velocity limit of the stopping power of a moving ion in a host. The model is parameter free, as its components are derived from ab initio-type calculations, is readily extended to the case of alloys, and is adequate for large-scale molecular dynamics computer simulations. We also show how this model removes some oversimplifications of the traditional ionic damped dynamics commonly used to describe situations beyond the Born-Oppenheimer approximation.

  • 3577.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Pan, Junyou
    Merck KGaA.
    Buchholz, Herwig
    Merck KGgA.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    White light-emitting electrochemical cell2011In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 3, no 9, p. 3384-3388Article in journal (Refereed)
    Abstract [en]

    We report a light-emitting electrochemical cell (LEC) with air-stable electrodes and a solution-processed single-layer active material that emits warm-white light (CIE coordinates = (0.39, 0.43); color rendering index =83) with significant brightness (B) at a low voltage. The carefully tuned trichromatic device exhibits a short turn-on time (5 s to B > 100 cd/m2), high efficiency (3.1 cd/A at B = 240 cd/m2) and good operational stability (17 h at B > 100 cd/m2). We also report a blue LEC with a highly respectable set of device properties in the form of a turn-on time of 5 s, an efficiency of 3.6 lm/W and 5.6 cd/A, and an uninterrupted operational lifetime of 25 h. Finally, by analyzing data from trichromatic and monochromatic devices as well as from the constituent fluorescent CPs, we are able to point out a viable path toward further improvements in the performance of the white-emitting LEC.

  • 3578.
    Tang, Shi
    et al.
    Umeå University, Sweden; LunaLEC AB, Sweden.
    Sandstrom, Andreas
    Umeå University, Sweden; LunaLEC AB, Sweden.
    Lundberg, Petter
    Umeå University, Sweden.
    Lanz, Thomas
    Umeå University, Sweden.
    Larsen, Christian
    Umeå University, Sweden; LunaLEC AB, Sweden.
    van Reenen, Stephan
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Kemerink, Martijn
    Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.
    Edman, Ludvig
    Umeå University, Sweden; LunaLEC AB, Sweden.
    Design rules for light-emitting electrochemical cells delivering bright luminance at 27.5 percent external quantum efficiency2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 1190Article in journal (Refereed)
    Abstract [en]

    The light-emitting electrochemical cell promises cost-efficient, large-area emissive applications, as its characteristic in-situ doping enables use of air-stabile electrodes and a solution-processed single-layer active material. However, mutual exclusion of high efficiency and high brightness has proven a seemingly fundamental problem. Here we present a generic approach that overcomes this critical issue, and report on devices equipped with air-stabile electrodes and outcoupling structure that deliver a record-high efficiency of 99.2 cd A(-1) at a bright luminance of 1910 cd m(-2). This device significantly outperforms the corresponding optimized organic light-emitting diode despite the latter employing calcium as the cathode. The key to this achievement is the design of the host-guest active material, in which tailored traps suppress exciton diffusion and quenching in the central recombination zone, allowing efficient triplet emission. Simultaneously, the traps do not significantly hamper electron and hole transport, as essentially all traps in the transport regions are filled by doping.

  • 3579.
    Tang, Shi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    Sandström, Andreas
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    Lundberg, Petter
    Lanz, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    LunaLEC AB.
    van Reenen, Stephan
    Kemerink, Martijn
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics. LunaLEC AB.
    Design rules for light-emitting electrochemical cells delivering bright luminance at 27.5 percent external quantum efficiency2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 1190Article in journal (Refereed)
    Abstract [en]

    The light-emitting electrochemical cell promises cost-efficient, large-area emissive applications, as its characteristic in-situ doping enables use of air-stabile electrodes and a solution-processed single-layer active material. However, mutual exclusion of high efficiency and high brightness has proven a seemingly fundamental problem. Here we present a generic approach that overcomes this critical issue, and report on devices equipped with air-stabile electrodes and outcoupling structure that deliver a record-high efficiency of 99.2 cd A(-1) at a bright luminance of 1910 cd m(-2). This device significantly outperforms the corresponding optimized organic light-emitting diode despite the latter employing calcium as the cathode. The key to this achievement is the design of the host-guest active material, in which tailored traps suppress exciton diffusion and quenching in the central recombination zone, allowing efficient triplet emission. Simultaneously, the traps do not significantly hamper electron and hole transport, as essentially all traps in the transport regions are filled by doping.

  • 3580.
    Tao, Quanzheng
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Salikhov, R.
    University of Duisburg Essen, Germany.
    Mockuté, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Farle, M.
    University of Duisburg Essen, Germany; IKBFU, Russia.
    Wiedwald, U.
    University of Duisburg Essen, Germany.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Thin film synthesis and characterization of a chemically ordered magnetic nanolaminate (V,Mn)(3)GaC22016In: APL MATERIALS, ISSN 2166-532X, Vol. 4, no 8, article id 086109Article in journal (Refereed)
    Abstract [en]

    We report on synthesis and characterization of a new magnetic nanolaminate (V,Mn)(3)GaC2, which is the first magnetic MAX phase of a 312 stoichiometry. Atomically resolved energy dispersive X-ray mapping of epitaxial thin films reveals a tendency of alternate chemical ordering between V and Mn, with atomic layers composed of primarily one element only. Magnetometry measurements reveal a ferromagnetic response between 50 K and 300 K, with indication of a magnetic ordering temperature well above room temperature. (C) 2016 Author(s).

  • 3581.
    Tarnavich, V.
    et al.
    Natl Res Ctr, Kurchatov Inst, Petersburg Nucl Phys Inst, Gatchina 188300, Russia..
    Tartakovskaya, E.
    Natl Acad Sci Ukraine, Inst Magnetism, UA-03142 Kiev, Ukraine.;Kiev Natl Univ, Inst High Technol, Glushkovaave 4-G, UA-03022 Kiev, Ukraine..
    Chetverikov, Yu.
    Natl Res Ctr, Kurchatov Inst, Petersburg Nucl Phys Inst, Gatchina 188300, Russia..
    Golub, V.
    Natl Acad Sci Ukraine, Inst Magnetism, UA-03142 Kiev, Ukraine..
    Lott, D.
    Helmholtz ZentrumGeesthacht, D-21502 Geesthacht, Germany..
    Chernenkov, Yu.
    Natl Res Ctr, Kurchatov Inst, Petersburg Nucl Phys Inst, Gatchina 188300, Russia..
    Devishvili, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Ukleev, V.
    Natl Res Ctr, Kurchatov Inst, Petersburg Nucl Phys Inst, Gatchina 188300, Russia.;RIKEN, Ctr Emergent Matter Sci, Wako, Saitama 3510198, Japan..
    Kapaklis, Vassilios
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Oleshkevych, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Fedorov, V.
    St Petersburg Acad Univ, St Petersburg 194021, Russia..
    Bairamukov, V.
    Natl Res Ctr, Kurchatov Inst, Petersburg Nucl Phys Inst, Gatchina 188300, Russia..
    Vorobiev, Alexei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Grigoriev, S.
    Natl Res Ctr, Kurchatov Inst, Petersburg Nucl Phys Inst, Gatchina 188300, Russia.;St Petersburg State Univ, St Petersburg 198504, Russia..
    Magnetic field induced chirality in Ho/Y multilayers with gradually decreasing anisotropy2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 1, article id 014415Article in journal (Refereed)
    Abstract [en]

    Metal rare-earth magnetic/nonmagnetic Ho/Y superlattice structures possess a coherent spin helix propagating through many superlattice layer repetitions. An externalmagnetic field applied in the film plane induces a nonzero average chirality of the helices. It is shown that the direction of the applied in-plane field can modify the value and sign of the chirality parameter.. The dependence of. on the relative angle of applied field during the field`-cooling procedure has an oscillatory character and can be described by simple sinusoidal function with p periodicity. The experimental finding is discussed from the point of view of an interbalance between Zeeman energy, magnetocrystalline anisotropy, and induced uniaxial anisotropy.

  • 3582. Tarnavich, V. V.
    et al.
    Lott, D.
    Mattauch, S.
    Oleshkevych, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Kapaklis, Vassilios
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Grigoriev, S. V.
    Field-induced chirality in the helix structure of Ho/Y multilayers2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 5, p. 054406-Article in journal (Refereed)
    Abstract [en]

    We study the net chirality in the spin helix structure of Ho/Y multilayers induced by an in-plane applied magnetic field. The lifting of degeneracy of the chiral symmetry was revealed by means of polarized neutron reflectometry. Three samples of different thicknesses of the Ho and Y layers were grown by molecular-beam epitaxy. The chiral states are degenerated upon zero field cooling below the critical temperature TN=115±3 K. The chirality parameter γ rises during the field cooling procedure in the field range from 0 to 1 T and saturates at a value of 0.12±0.01. The chirality appears stepwise below TN and depends weakly on temperature. The phenomenon is interpreted in terms of the Dzyaloshinskii-Moriya interaction appearing at the interface between the Ho and Y layers.

  • 3583.
    Tasnadi, Ferenc
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Höglund, Carina
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Wingqvist, Gunilla
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Birch, Jens
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Origin of the Anomalous Piezoelectric Response in Wurtzite ScxAl1-xN Alloys2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 13, p. 137601-Article in journal (Refereed)
    Abstract [en]

    The origin of the anomalous, 400% increase of the piezoelectric coefficient in ScxAl1-xN alloys is revealed. Quantum mechanical calculations show that the effect is intrinsic. It comes from a strong change in the response of the internal atomic coordinates to strain and pronounced softening of C-33 elastic constant. The underlying mechanism is the flattening of the energy landscape due to a competition between the parent wurtzite and the so far experimentally unknown hexagonal phases of the alloy. Our observation provides a route for the design of materials with high piezoelectric response.

  • 3584. Tatsumi, Kazuyoshi
    et al.
    Muto, Shunsuke
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Energy Loss by Channeled Electrons: A Quantitative Study on Transition Metal Oxides2013In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 19, no 6, p. 1586-1594Article in journal (Refereed)
    Abstract [en]

    Electron energy-loss spectroscopy (EELS) attached to current   transmission electron microscopes can probe not only element-selective   chemical information, but also site-selective information that depends   on the position that a specific element occupies in a crystal lattice.   The latter information is exploited by utilizing the Bloch waves   symmetry in the crystal, which changes with its orientation with respect   to the incident electron wave (electron channeling). We demonstrate the   orientation dependence of the cross-section of the electron energy-loss   near-edge structure for particular crystalline sites of spinel ferrites,   by quantitatively taking into account the dynamical diffraction effects   with a large number of the diffracted beams. The theoretical results are   consistent with a set of experiments in which the transition metal sites   in spinel crystal structures are selectively excited. A new measurement   scheme for site-selective EELS using a two-dimensional   position-sensitive detector is proposed and validated by theoretical   predictions and trial experiments.

  • 3585.
    Tavabi, Amir H.
    et al.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52428 Julich, Germany.;Forschungszentrum Julich, Peter Grunberg Inst, D-52428 Julich, Germany..
    Beleggia, Marco
    Tech Univ Denmark, Ctr Elect Nanoscopy, DK-2800 Lyngby, Denmark..
    Migunov, Vadim
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52428 Julich, Germany.;Forschungszentrum Julich, Peter Grunberg Inst, D-52428 Julich, Germany..
    Savenko, Alexey
    FEI Co, Achtseweg Noord 5, NL-5600 KA Eindhoven, Netherlands..
    Öktem, Ozan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.). KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM.
    Dunin-Borkowski, Rafal E.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52428 Julich, Germany.;Forschungszentrum Julich, Peter Grunberg Inst, D-52428 Julich, Germany..
    Pozzi, Giulio
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52428 Julich, Germany.;Forschungszentrum Julich, Peter Grunberg Inst, D-52428 Julich, Germany.;Univ Bologna, Dept Phys & Astron, Viale B Pichat 6-2, I-40127 Bologna, Italy..
    Tunable Ampere phase plate for low dose imaging of biomolecular complexes2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 5592Article in journal (Refereed)
    Abstract [en]

    A novel device that can be used as a tunable support-free phase plate for transmission electron microscopy of weakly scattering specimens is described. The device relies on the generation of a controlled phase shift by the magnetic field of a segment of current-carrying wire that is oriented parallel or antiparallel to the electron beam. The validity of the concept is established using both experimental electron holographic measurements and a theoretical model based on Ampere's law. Computer simulations are used to illustrate the resulting contrast enhancement for studies of biological cells and macromolecules.

  • 3586. Tchaplyguine, Maxim
    et al.
    Andersson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Zhang, Chaofan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Svensson, Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Core-shell structure disclosed in self-assembled Cu-Ag nanoalloy particles—explanation for enhanced catalytic activity?Manuscript (preprint) (Other academic)
    Abstract [en]

    Core-shell segregation of copper and silver in self-assembled, free nanoparticles is established by means of electron spectroscopy using different photon energies. The nanoparticles are formed from metal-atom mixed vapor created by sputtering of a bimetallic sample. Even at dominating copper concentration in the primary vapor the surface of the nanoparticles is composed of only silver. These conclusions are based on the analysis of the photon-energy-dependent changes of the Cu 3d and Ag 4d photoelectron spectra. The role of such segregation is discussed in connection to the suggested enhanced catalytic properties of Cu-Ag nanoparticles.

  • 3587. Tchaplyguine, Maxim
    et al.
    Öhrwall, Gunnar
    Huttula, Marko
    Mikkelä, Mikko-Heikki
    Urpelainen, Samuli
    Osmekhin, Sergey
    Caló, Antonio
    Aksela, Seppo
    Aksela, Helena
    Andersson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Svensson, Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Valence-band narrowing and metallic-screening disappearance in the metal-to-insulator transition in small Pb clusters—as seen by photoelectron spectroscopyManuscript (preprint) (Other academic)
    Abstract [en]

    A metal-to-insulator transition in small Pb clusters within the size range from a few tens of atoms up to ~100 atoms is investigated using synchrotron-based photoelectron spectroscopy. The electronic structure is seen to differ increasingly from that of the solid when the cluster size decreases. With the cluster size decrease the valence band narrows gradually -down to 25% of that of the solid-state at the smallest size of few tens of atoms. Simultaneously the Fermi-edge energy increases. The Pb 5d core level binding energy also increases and the spectral features broaden and change the shape. The changes observed for the valence and for the 5d energies and shapes are consistent with the picture of the loss of metallicity in Pb below the critical size of 20-30 atoms/cluster.

  • 3588.
    Teber, S.
    et al.
    Université Pierre et Marie Curie, France.
    Holmqvist, Cecilia
    Chalmers University of Technology.
    Fogelström, M.
    Chalmers University of Technology, France.
    Transport and magnetization dynamics in a superconductor/single-molecule magnet/superconductor junction2010In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 81, article id 174503Article in journal (Refereed)
    Abstract [en]

    We study dc-transport and magnetization dynamics in a junction of arbitrary transparency consisting of two spin-singlet superconducting leads connected via a single classical spin precessing at the frequency Ω. The presence of the spin in the junction provides different transmission amplitudes for spin-up and spin-down quasiparticles as well as a time-dependent spin-flip transmission term. For a phase-biased junction, we show that a steady-state superconducting charge current flows through the junction and that an out-of-equilibrium circularly polarized spin current, of frequency Ω, is emitted in the leads. Detailed understanding of the charge and spin currents is obtained in the entire parameter range. In the adiabatic regime, ℏΩ⪡2Δ, where Δ is the superconducting gap, and for high transparencies of the junction, a strong suppression of the current takes place around φ≈0 due to an abrupt change in the occupation of the Andreev bound states. At higher values of the phase and/or precession frequency, extended (quasiparticlelike) states compete with the bound states in order to carry the current. Well below the superconducting transition, these results are shown to be weakly affected by the backaction of the spin current on the dynamics of the precessing spin. Indeed, we show that the Gilbert damping due to the quasiparticle spin current is strongly suppressed at low temperatures, which goes along with a shift of the precession frequency due to the condensate. The results obtained may be of interest for ongoing experiments in the field of molecular spintronics.

  • 3589.
    Teber, S.
    et al.
    Universités Paris 6, 7 et CNRS, France ; CNRS and Université Joseph Fourier, France.
    Holmqvist, Cecilia
    CNRS and Université Joseph Fourier, France ; Chalmers University of Technology .
    Houzetd, M.
    INAC/SPSMS, France.
    Feinberg, D.
    CNRS and Université Joseph Fourier, France.
    Fogelström, M.
    Chalmers University of Techology.
    Josephson current through a precessing classical spin2009In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 404, p. 527-529Article in journal (Refereed)
    Abstract [en]

    A study of the dc Josephson current between two superconducting leads in the presence of a precessingclassical spin is presented. The precession gives rise to a time-dependent tunnel potential which notonly implies different tunneling probabilities for spin-up and spin-down quasiparticles, but introducesalso a time-dependent spin-flip term. We provide an exact general analytic solution for the out-of-equilibrium steady-state permanent current between two spin-singlet superconductors as a functionof the superconducting phase difference, the precession frequency and for arbitrary junction transparency.As an application we focus on the effects of the spin-flip term alone and show that the magnitude andnature of the Josephson current are indeed strongly affected by the precession of the classical spin.

  • 3590.
    Tegenfeldt, J
    et al.
    University of Uppsala.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology. University of Uppsala.
    Svensson, C
    University of Lund.
    Disorder dynamics in solid 9‐hydroxyphenalenone1991In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 95, p. 2696-2701Article in journal (Refereed)
    Abstract [en]

    1 H nuclear magnetic resonance(NMR)spectra and spin‐lattice relaxation data as well as 1 H decoupled 13C spectra have been utilized to study the dynamics of the molecular disorder in solid 9‐hydroxyphenalenone. In the room‐temperature phase—stable between 255 and 380 K—the protonspectrum is narrowed compared to the spectrum of a static structure. This is consistent with a dynamically disordered structure where one of the two nonequivalent molecules reorients rapidly between its two possible equilibrium orientations. The proton spin‐lattice relaxation has a maximum of 7.2 s−1 in the same phase at about 355 K, in close agreement with a value of 7.6 s−1 calculated from the dynamical disorder model. The 1 H decoupled 13C powderspectrum in the room‐temperature phase is also consistent with this picture. Above the 385 K phase transition, the 13C powderspectrum is approaching axial symmetry, proving that all molecules reorient rapidly in that phase.

  • 3591.
    Tengdin, Phoebe
    et al.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    You, Wenjing
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Chen, Cong
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Shi, Xun
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Zusin, Dmitriy
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Zhang, Yingchao
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Gentry, Christian
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Blonsky, Adam
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Keller, Mark
    NIST, 325 Broadway, Boulder, CO 80305 USA.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kapteyn, Henry C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Tao, Zhensheng
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Murnane, Margaret M.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA;Univ Colorado, JILA, Boulder, CO 80309 USA;NIST, Boulder, CO 80309 USA.
    Critical behavior within 20 fs drives the out-of-equilibrium laser-induced magnetic phase transition in nickel2018In: Science Advances, ISSN 0036-8156, E-ISSN 2375-2548, Vol. 4, no 3, article id eaap9744Article in journal (Refereed)
    Abstract [en]

    It has long been known that ferromagnets undergo a phase transition from ferromagnetic to paramagnetic at the Curie temperature, associated with critical phenomena such as a divergence in the heat capacity. A ferromagnet can also be transiently demagnetized by heating it with an ultrafast laser pulse. However, to date, the connection between out-of-equilibrium and equilibrium phase transitions, or how fast the out-of-equilibrium phase transitions can proceed, was not known. By combining time-and angle-resolved photoemission with time-resolved transverse magneto-optical Kerr spectroscopies, we show that the same critical behavior also governs the ultrafast magnetic phase transition in nickel. This is evidenced by several observations. First, we observe a divergence of the transient heat capacity of the electron spin system preceding material demagnetization. Second, when the electron temperature is transiently driven above the Curie temperature, we observe an extremely rapid change in the material response: The spin system absorbs sufficient energy within the first 20 fs to subsequently proceed through the phase transition, whereas demagnetization and the collapse of the exchange splitting occur on much longer, fluence-independent time scales of similar to 176 fs. Third, we find that the transient electron temperature alone dictates the magnetic response. Our results are important because they connect the out-of-equilibrium material behavior to the strongly coupled equilibrium behavior and uncover a new time scale in the process of ultrafast demagnetization.

  • 3592. Terentev, Ya. V.
    et al.
    Toropov, A. A.
    Sorokin, S. V.
    Lebedev, A. V.
    Ivanov, S. V.
    Kopev, P. S.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Functional Electronic Materials.
    Monemar, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Semimagnetic ZnMnSe/CdSe Fractional Monolayer Superlattice as an Injector of Spin-Polarized Carriers2002In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 229, no 2, p. 765-768Article in journal (Refereed)
    Abstract [en]

    We report on effective injection of spin-oriented carriers from a semimagnetic semiconductor structure to a non-magnetic ZnCdSe/ZnSe quantum well (QW). A short-period ZnMnSe/CdSe fractional monolayer superlattice was used as a spin injector. The carriers are photo-generated in the semimagnetic region, spin-polarized via the effect of giant Zeeman splitting and then injected into the non-magnetic QW. The spin injection efficiency was estimated by circular polarization measurements of recombination emission from the QW. The maximal detected degree of the spin polarization is about 25%.

  • 3593. Terentyev, D. A.
    et al.
    Klaver, T. P. C.
    Olsson, Pär
    School of Mathematics and Physics, Queen's University Belfast, United Kingdom.
    Marinica, M. -C.
    Willaime, F.
    Domain, C.
    Malerba, L.
    Self-trapped interstitial-type defects in iron2008In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 100, no 14Article in journal (Refereed)
    Abstract [en]

    Small interstitial-type defects in iron with complex structures and very low mobilities are revealed by molecular dynamics simulations. The stability of these defect clusters formed by nonparallel < 110 > dumbbells is confirmed by density functional theory calculations, and it is shown to increase with increasing temperature due to large vibrational formation entropies. This new family of defects provides an explanation for the low mobility of clusters needed to account for experimental observations of microstructure evolution under irradiation at variance with the fast migration obtained from previous atomistic simulations for conventional self-interstitial clusters.

  • 3594. Terentyev, D.
    et al.
    Bonny, G.
    Castin, N.
    Domain, C.
    Malerba, L.
    Olsson, Pär
    Dept. MMC, EDF-R and D, Site des Renardières, France.
    Moloddtsov, V.
    Pasianot, R. C.
    Further development of large-scale atomistic modelling techniques for Fe-Cr alloys2011In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 409, no 2, p. 167-175Article in journal (Refereed)
    Abstract [en]

    In this paper we review the current status of our efforts to model the Fe-Cr system, which is a model alloy for high-Cr ferritic-martensitic steels, using large-scale atomistic methods. The core of such methods are semi-empirical interatomic potentials. Here we discuss their performance with respect to the features that are important for an accurate description of radiation effects in Fe-Cr alloys. We describe their most recent improvements regarding macroscopic thermodynamic properties as well as microscopic point-defect properties. Furthermore we describe a new type of large-scale atomistic kinetic Monte Carlo (AKMC) approach driven by an artificial neural network (ANN) regression method to generate the local migration barrier for a defect accounting for the local chemistry around it. The results of the thermal annealing of the Fe-20Cr alloy modelled using this AKMC approach, parameterized by our newly developed potential, were found to be in very good agreement with experimental data. Furthermore the interaction of a 1/2 (1 1 1) screw dislocation with Cr precipitates as obtained from the AKMC simulations was studied using the same potential. In summary, we critically discuss our current achievements, findings and outline issues to be addressed in the near future development.

  • 3595. Terentyev, D.
    et al.
    Olsson, Pär
    EDF R&D, Dept Mat & Mecan Composants, France.
    Aspects Of Radiation Damage Effects In Fe-Cr Alloys From The Point Of View Of Atomistic Modeling2009In: PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, ISSN 1562-6016, no 4, p. 68-79Article in journal (Refereed)
    Abstract [en]

    Fe-Cr alloys are the basis of high-Cr ferritic steels, which are the candidates for the structural materials for near future power plants. Recently, a significant effort has been put in the development of theoretical models dealing with the response of Fe-Cr alloys to irradiation. Here, we give a brief overview of the current level of understanding of radiation damage in Fe-Cr alloys, based on the most recent results. In particular, we review and summarize data obtained using different atomistic modelling techniques in order to refine the most important findings achieved over the past few years.

  • 3596. Terentyev, D.
    et al.
    Olsson, Pär
    Department Matériaux et Méchanique des Composants, EFD-R and D, Les Renardieres, France.
    Klaver, T. P. C.
    Malerba, L.
    On the migration and trapping of single self-interstitial atoms in dilute and concentrated Fe-Cr alloys: Atomistic study and comparison with resistivity recovery experiments2008In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 43, no 4, p. 1183-1192Article in journal (Refereed)
    Abstract [en]

    Atomistic simulations have been used to characterize the mobility of single self interstitial atoms (SIAs) in Fe-Cr alloys of different compositions. Density functional theory (DFT) results concerning the interaction energies between an SIA and Cr atoms in different configurations and relative positions have been extended to concentrated alloys by using an empirical potential (EP). This EP, fitted to a set of DFT data so as to provide a correct heat of mixing and point defect features, has been further validated. Static calculations using the EP allowed the existence of configuration traps for SIAs to be identified and their strength and concentration to be assessed. Dynamic simulations were used to estimate the diffusion coefficient of the SIA, as well as to characterize the primary damage state after low-temperature electron irradiation (1-5 MeV), in Fe-Cr alloys of different Cr content. The results correlate with available experimental data and provide a qualitative and partially also quantitative explanation for the observed differences in the resistivity recovery stages in diluted and concentrated Fe-Cr alloys of different composition.

  • 3597. Terentyev, D.
    et al.
    Olsson, Pär
    Département MMC, EDF-R and D, Les Renardieres, France.
    Malerba, L.
    Diffusion of 3D-migrating self-interstitial clusters in diluted and concentrated Fe-Cr alloys2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 386-88, no C, p. 140-142Article in journal (Refereed)
    Abstract [en]

    We show, using atomic-level simulations, that the mobility of small 3D-migrating self-interstitial atom (SIA) clusters produced in displacement cascades is significantly reduced in concentrated Fe-Cr alloys (up to 15%Cr) as compared to Fe. The presence of alpha' precipitates, on the other hand, is only expected to provide scattering centers for interstitial-type defects, whose formation inside the precipitates is energetically unfavorable. The significant reduction in the mobility of 3D-migrating SIA clusters is expected to have an important impact on the microstructure evolution of high-Cr steels, depending on Cr concentration.

  • 3598. Terentyev, D.
    et al.
    Olsson, Pär
    Physique des Solides Irradiés et des Nanostructures, CP23, Université Libre de Bruxelles.
    Malerba, L.
    Barashev, A. V.
    Characterization of dislocation loops and chromium-rich precipitates in ferritic iron-chromium alloys as means of void swelling suppression2007In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 362, no 2-3, p. 167-173Article in journal (Refereed)
    Abstract [en]

    We have used both ab initio and empirical potential based molecular dynamics and static calculations to parameterize a model accounting for the mobility of self-interstitial clusters and small dislocation loops in Fe-Cr alloys depending on Cr content. Particularly, we have considered the interval of 5-15% of Cr, corresponding to the typical concentration of Cr in ferritic/martensitic steels. The mobility of self-interstitial clusters and small dislocation loops was found to be strongly reduced in the presence of Cr due to attractive interaction between self-interstitials and Cr atoms, whereas Cr-rich precipitates act as repulsive obstacles. The results obtained allow the experimental trend of swelling measurements in neutron and high-energy electron irradiated Fe-Cr alloys to be interpreted and explained.

  • 3599. Terentyev, Dmitry
    et al.
    Malerba, Lorenzo
    Klaver, Peter
    Olsson, Pär
    EDF, Department Matériaux et Méchanique des Composants, Les Renardieres, France.
    Formation of stable sessile interstitial complexes in reactions between glissile dislocation loops in bcc Fe2008In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 382, no 2-3, p. 126-133Article in journal (Refereed)
    Abstract [en]

    Clusters of self-interstitial atoms (loops) are commonly observed in the microstructure of irradiated metals. These clusters can be formed directly in high-energy displacement cascades or by growth as a result of interaction between individual self interstitials. The majority of these clusters have features of glissile dislocation loops and migrate by fast one-dimensional glide. In this paper, we present results of a systematic molecular dynamics (MD) study of reactions involving glissile interstitial loops. By the example of bcc iron we demonstrate that the reactions can produce a number of specific, stable microstructural features, with different properties compared to the reactants. Namely, the reactions between the most common glissile clusters of < 111 > crowdions can result in coarsening or formation of immobile self interstitial complexes. The coarsening leads to a decrease of the total dislocation line length and therefore is favourable. The structure and stability of the junction formed in the reactions has been studied using many body potentials and density functional theory (DFT) techniques. No evidence of the formation of a < 100 > loop from two glissile < 111 > clusters was found among the studied reactions. The immobile self interstitial complexes that form as a result of these reaction have, however, high binding energies, of the order of tens of eV, implying that a relatively long life time should be assigned to the resulting configurations and therefore that such objects are expected to contribute to the evolution of the microstructure under irradiation.

  • 3600. Tesch, M. F.
    et al.
    Legut, D.
    Mertins, H. -Ch.
    Gilbert, M. C.
    Jansing, C.
    Hamrle, J.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Buergler, D. E.
    Schneider, C. M.
    Gaupp, A.
    Berges, U.
    Magnetocrystalline anisotropy in x-ray magnetic linear dichroism at the 3 p edges of crystalline Fe thin films2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 14, p. 140404-Article in journal (Refereed)
    Abstract [en]

    X-ray magnetic linear dichroism spectra measured in reflection (XMLD-R) on crystalline bcc Fe thin films across the 3 p absorption edges are reported. A series of measurements with varying orientation of the electric field vector of the linear polarized synchrotron radiation with respect to the crystal axes reveals a strong magnetocrystalline anisotropy in the XMLD-R spectra. The spectra agree well with theoretical spectra calculated within the framework of the density-functional theory accounting for the spin-orbital and exchange splitting of the 3 p semicore states on an equal footing.

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