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  • 3551. Ulyanov, A.N.
    et al.
    Maksimov, Igor S.
    Nyeanchi, Emmanuel B.
    Umeå University, Faculty of Science and Technology, Physics.
    Yu, Seong-Cho
    Medvedev, Y.V.
    Starostyuk, N.Y.
    Sundqvist, Bertil
    Umeå University, Faculty of Science and Technology, Physics.
    Crystal symmetry and pressure effects on the properties of mixed-valence manganites2003In: Journal of Magnetism and Magnetic Materials vol. 258-259, Special Issue SI: Proceedings of the 2nd Moscow International Symposium on Magnetism, Amsterdam: Elsevier B.V. , 2003, p. 312-314Conference paper (Refereed)
    Abstract [en]

    A lattice structure effect on the magnetic and magnetotransport properties of La0.7Ca(0.3-x)SrxMnO3 lanthanum manganites have been studied. The Curie temperature pressure coefficient increased almost linearly under an applied pressure as dTc/dP=14K/GPa and as dTc/dP=7.5K/GPa in the orthorhombic and rhombohedral structures,respectively. This is caused by the different pressure effect on the Mn–O bond distances and on the Mn–O–Mn bond angles in those phases. The anomalous low value of dTc/dP(=3.5K/GPa) for La0.7Ca0.15Sr0.15MnO3 composition and a jump of the magnetoresistance maximum value at the concentrational Pbnm2R%3c phase transition were observed and discussed.

  • 3552. Uneus, L
    et al.
    Nakagomi, S
    Linnarsson, M
    KTH, School of Information and Communication Technology (ICT).
    Janson, M S
    Svensson, B G
    Yakimova, R
    Syvajarvi, M
    Henry, A
    Janzen, E
    Ekedahl, L G
    Lunstrom, I
    Spetz, A L
    The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures2002In: SILICON CARBIDE AND RELATED MATERIALS 2001, PTS 1 AND 2, PROCEEDINGS, 2002, Vol. 389-3, p. 1419-1422Conference paper (Refereed)
    Abstract [en]

    We present here the effect of a hydrogen anneal at 600degreesC for Schottky sensor devices based on n- and p-type 4H SiC. The devices have gate contacts of Ta/Pt, or TaSix/Pt. The catalytic metal gate dissociates hydrogen and thus promotes diffusion of hydrogen atoms into the SiC, where the atoms will trap or react with different impurities, defects or surface states. This will change parameters such as the carrier concentrations, the defect density of the material or the surface resistivity at the SiC/SiO2 interface. The current-voltage and the capacitance-voltage characteristics were measured before and after annealing in hydrogen and oxygen containing atmosphere, and the results show a reversible effect in the I-V characteristics.

  • 3553.
    Urbaniak, A.
    et al.
    Warsaw Univ Technol, Fac Phys, Koszykowa 75, PL-00662 Warsaw, Poland..
    Macielak, K.
    Warsaw Univ Technol, Fac Phys, Koszykowa 75, PL-00662 Warsaw, Poland..
    Igalson, M.
    Warsaw Univ Technol, Fac Phys, Koszykowa 75, PL-00662 Warsaw, Poland..
    Szaniawski, Piotr
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Defect levels in Cu(In,Ga)Se-2 studied using capacitance and photocurrent techniques2016In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 28, no 21, article id 215801Article in journal (Refereed)
    Abstract [en]

    This work contributes to the discussion on defect levels in Cu(In, Ga)Se-2 photovoltaic material. CuInSe2- and Cu(In, Ga)Se-2-based Schottky junctions, solar cells and thin films were investigated using complementary capacitance and current spectroscopic techniques. Depending on the applied technique and type of investigated structure, six different signals were observed. Out of the signals identified, three were ascribed to responses from bulk defects-two electron and one hole trap. The remainder were discussed in light of available in-literature models including carrier mobility freeze-out and non-ohmic back junction.

  • 3554.
    Uždavinys, Tomas Kristijonas
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Becerra, D. L.
    Ivanov, Ruslan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Denbaars, S. P.
    Nakamura, S.
    Speck, J. S.
    Marcinkevicius, Saulius
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Influence of well width fluctuations on recombination properties in semipolar InGaN quantum wells studied by time- and spatially-resolved near-field photoluminescence2017In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, no 9, article id 3116Article in journal (Refereed)
    Abstract [en]

    Scanning near-field photoluminescence spectroscopy has been applied to distinguish the relevance of quantum well (QW) alloy composition and well width fluctuations on emission linewidth and recombination times in semipolar (2021) plane InGaN QWs. It has been found that well width fluctuations, compared to variations of InGaN alloy composition, play a negligible role in defining the photoluminescence linewidth. However, the well width strongly affects the recombination times. Prolonged radiative and nonradiative carrier lifetimes in wide QWs have been attributed to electron and hole separation by in-plane electric fields caused by nonplanarity of QW interfaces.

  • 3555.
    Vagin, Mikhail
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Sekretareva, Alina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. Department of Chemistry, Stanford University, Stanford, USA.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Håkansson, Anna
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Iakimov, Tihomir
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphensic AB, Teknikringen 1F, Linköping, Sweden.
    Syväjärvi, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphensic AB, Teknikringen 1F, Linköping, Sweden.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Graphensic AB, Teknikringen 1F, Linköping, Sweden.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, Faculty of Science & Engineering.
    Monitoring of epitaxial graphene anodization2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 238, p. 91-98Article in journal (Refereed)
    Abstract [en]

    Anodization of a graphene monolayer on silicon carbide was monitored with electrochemical impedance spectroscopy. Structural and functional changes of the material were observed by Raman spectroscopy and voltammetry. A 21 fold increase of the specific capacitance of graphene was observed during the anodization. An electrochemical kinetic study of the Fe(CN)(6)(3) (/4) redox couple showed a slow irreversible redox process at the pristine graphene, but after anodization the reaction rate increased by several orders of magnitude. On the other hand, the Ru(NH3) (3+/2+)(6) redox couple proved to be insensitive to the activation process. The results of the electron transfer kinetics correlate well with capacitance measurements. The Raman mapping results suggest that the increased specific capacitance of the anodized sample is likely due to a substantial increase of electron doping, induced by defect formation, in the monolayer upon anodization. The doping concentration increased from less than 1 x 10(13) of the pristine graphene to 4-8 x 10(13) of the anodized graphene. (C) 2017 Elsevier Ltd. All rights reserved.

    The full text will be freely available from 2019-04-04 13:36
  • 3556.
    Vagin, Mikhail Yu
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Sekretareva, Alina
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, Faculty of Science & Engineering.
    Lindgren, Petter
    Håkansson, Anna
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Chemical and Optical Sensor Systems. Linköping University, Faculty of Science & Engineering.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Biosensors and Bioelectronics. Linköping University, Faculty of Science & Engineering.
    Syväjärve, Mikael
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Direct bioelectrocatalysis on anodized epitaxial graphene2015In: Program of the XXIII International Symposium on Bioelectrochemistry and Bioenergetics of the Bioelectrochemical Society14-18 June, 2015Malmö, Sweden, Lausanne: Bioelectrochemical Society , 2015, p. 170-170Conference paper (Other academic)
    Abstract [en]

    Graphene as a nanomaterial consisting of a single layer sheets of atoms of carbon in hexagonal arrangement is making a significant impact in variety of technologies such as energy storage and chemical analysis. The significant attention paid to this thinnest nanomaterial resulted in thousands of patent applications is due to its staggering properties. Due to the planar conjugation of the sp2bonds in graphene, two-dimensional electrical conduction is highly efficient. On the contrary, the efficiency of electron exchange at the out-of-plane of the graphene sheet is small. The significant difference of the densities of electronic states at in-plane and out-of-plane of graphene sheet determines two distinct structural contributions (basal and edge plane respectively) to the behavior of all graphitic materials yielding the chemical and electrochemical anisotropy. Being the simplest building block of graphitic materials, graphene offers the possibility to study the behavior on the simplest level of structural organization. However, the major effort of the recent electrochemical studies of graphene were done using a bulk materials based on graphene flakes possessing the domination of edges of high reactivity. The planar orientation of graphene sheets with controllable exposure of basal plane is achievable via the growth by chemical vapor deposition or by epitaxial flash annealing on crystalline structures of silicon carbide. The slow growth of graphene onto crystalline support during annealing in the inert atmosphere results in a development of a high quality graphene monolayer attached to the solid insulating support. The creation of sp3-type reactive defects on the basal plane of graphite can be achieved by anodization at high anodic potentials.

    We developed the procedure for the real-time monitoring of epitaxial graphene anodization. The changes of electrochemical properties of graphene monolayer with anodization have been comparatively investigated by electrochemical methods. The estimation of specific capacitance in pure electrolyte and in conditions of Faradaic process has been carried out. Finally, the direct electrocatalysis of laccase (Trametes versicolor) has been used as an electrode reaction to probe the reactivities of anodized epitaxial graphene and conventional carbon materials.

  • 3557.
    Vaitheeswaran, Ganapathy
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kanchana, Venkatakrishnan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Electronic structure of the ferromagnetic double-perovskites Sr2CrReO6, Sr2CrWO6, and Ba2FeReO62006In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 29, no 1, p. 50-53Article in journal (Refereed)
    Abstract [en]

    We have studied the electronic structure of the ferromagnetic double perovskites Sr2CrReO6, Sr2CrWO6 and Ba2FeReO6 by means of a full-potential linear muffin-tin orbital density-functional method. Our scalar-relativistic calculations predict these compounds to be half-metallic with a total magnetic moment of 1, 2, and 3 νB respectively. However, when the spin-orbit coupling is included, the 5d transition Re and W ions exhibit substantial unquenched orbital magnetic moments, resulting in a significant increase of the total magnetic moment. The half-metallic gap turns into a pseudo-gap in Sr 2CrReO6 and Ba2FeReO6 when the spin-orbit coupling is included whereas Sr2CrWO6 remains half-metallic even with spin-orbit coupling. The calculated spin and orbital magnetic moments agrees well with the recent experimental XMCD measurements.

  • 3558.
    Vaitheeswaran, Ganapathy
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Kanchana, Venkatakrishnan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Pseudo-half-metallicity in the double perovskite Sr2CrReO6 from density-functional calculations2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 3Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the spintronic material Sr2CrReO6 is studied by means of full-potential linear muffin-tin orbital method. Scalar relativistic calculations predict Sr2CrReO6 to be half-metallic with a magnetic moment of 1 muB. When spin-orbit coupling is included, the half-metallic gap closes into a pseudo-gap, and an unquenched rhenium orbital moment appears, resulting in a significant increase of the total magnetic moment to 1.28 AB. This moment is significantly larger than the experimental moment of 0.9 mu(B). A possible explanation of this discrepancy is that the anti-site disorder in Sr2CrReO6 is significantly larger than hitherto assumed.

  • 3559. Vaitkus, J.
    et al.
    Baubinas, R.
    Kazlauskiene, V.
    Kuciauskas, D.
    Miskinis, J.
    Karlsson, U.
    Hammar, M.
    KTH, Superseded Departments, Physics.
    Göthelid, M.
    Björqvist, M.
    Lindberg, E.
    Scanning tunneling microscopy of CdSe single crystal cleaved and "real" surface1994In: Journal of Crystal Growth, ISSN 00220248 (ISSN), Vol. 138, no 1-4, p. 545-549Article in journal (Refereed)
    Abstract [en]

    Ultrahigh vacuum-cleaved and as-grown surfaces of CdSe single crystals were investigated by scanning tunneling microscopy. The single crystals were grown by Reynolds-Green method. Striations and terrace-step structure have been found. The surface atomic geometry was found and investigated. The (1120) face geometry (structure formed by elementary cell of 0.75 × 0.7 nm2) as well as other type structures (e.g., 2.1 × 0.75 nm2 elementary cell) have been determined. The variations of the band gap at the surface have been found. The band values in the range 2.0-2.6 eV on a cleaved surface and 1.1-2.0 eV on an as-grown surface were measured and explained as being the influence of surface relaxation and gas adsorption. © 1994.

  • 3560.
    Valenta, Jan
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Juhasz, Robert
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Photoluminescence spectroscopy of single silicon quantum dots2002In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 80, no 6, p. 1070-1072Article in journal (Refereed)
    Abstract [en]

    Photoluminescence (PL) from single silicon quantum dots have been recorded and spectrally resolved at room temperature. The Si nanocrystals (NCs) were fabricated using electron-beam lithography and reactive ion etching resulting in Si nanopillars that were subsequently oxidized to produce luminescent silicon cores. The NCs are organized in a regular matrix which enables repeated observation of a specific single NC. By reflection and PL imaging, the emission is shown to originate from the Si nanopillars. The single-NC PL spectrum has a single band with a width of similar to130 meV. The emission is polarized in arbitrary directions suggestive of geometrical differences in the shape of the nanocrystals. The quantum efficiency of the PL has been found to reach as much as 35% for some nanocrystals. Our experiments support the quantum-confinement model for the PL emission of Si nanocrystals and elucidate the critical role of defect passivation.

  • 3561.
    Valenti, Marco
    et al.
    Delft University of Technology, Netherlands.
    Venugopal, Anirudh
    Delft University of Technology, Netherlands.
    Tordera, Daniel
    Linköping University, Department of Science and Technology. Linköping University, Faculty of Science & Engineering.
    Jonsson, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Biskos, George
    Delft University of Technology, Netherlands; Cyprus Institute, Cyprus.
    Schmidt-Ott, Andreas
    Delft University of Technology, Netherlands.
    Smith, Wilson A.
    Delft University of Technology, Netherlands.
    Hot Carrier Generation and Extraction of Plasmonic Alloy Nanoparticles2017In: ACS Photonics, E-ISSN 2330-4022, Vol. 4, no 5, p. 1146-1152Article in journal (Refereed)
    Abstract [en]

    The conversion of light to electrical and chemical energy has the potential to provide meaningful advances to many aspects of daily life, including the production of energy, water purification, and optical sensing. Recently, plasmonic nanoparticles (PNPs) have been increasingly used in artificial photosynthesis (e.g., water splitting) devices in order to extend the visible light utilization of semiconductors to light energies below their band gap. These nanoparticles absorb light and produce hot electrons and holes that can drive artificial photosynthesis reactions. For n-type semiconductor photoanodes decorated with PNPs, hot charge carriers are separated by a process called hot electron injection (HEI), where hot electrons with sufficient energy are transferred to the conduction band of the semiconductor. An important parameter that affects the HEI efficiency is the nanoparticle composition, since the hot electron energy is sensitive to the electronic band structure of the metal. Alloy PNPs are of particular importance for semiconductor/PNPs composites, because by changing the alloy composition their absorption spectra can be tuned to accurately extend the light absorption of the semiconductor. This work experimentally compares the HEI efficiency from Ag, Au, and Ag/Au alloy nanoparticles to TiO2 photoanodes for the photoproduction of hydrogen. Alloy PNPs not only exhibit tunable absorption but can also improve the stability and electronic and catalytic properties of the pure metal PNPs. In this work, we find that the Ag/Au alloy PNPs extend the stability of Ag in water to larger applied potentials while, at the same time, increasing the interband threshold energy of Au. This increasing of the interband energy of Au suppresses the visible-light induced interband excitations, favoring intraband excitations that result in higher hot electron energies and HEI efficiencies.

  • 3562.
    Valter, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Thermal Conductivity of Uranium Mononitride2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Thermal conductivity is a crucial parameter for nuclear fuel, as it sets an upper limit on reactor operating temperature to have safety margins. Uranium mononitride (UN) is a prospective fuel for fast reactors, for which limited experimental studies have been conducted, compared to the currently dominating light-water reactor fuel, uranium dioxide. The aim of this thesis is to determine the thermal conductivity in UN and to determine its porosity dependence. This was done by manufacturing dense and porous high-purity samples of UN and examining them with laser flash analysis, which with data on specific heat and thermal expansion gives the thermal conductivity. To analyse the result, a theoretical study of the phenomenology of thermal conductivity as well as a review and comparison with previous investigations were carried out. The porosity range was 0.1–31% of theoretical density. Thermal diffusivity data from laser flash analysis, thermal expansion data and specific heat data was collected for 25–1400 C. The laser flash data had high discrepancy at higher temperatures due to thermal instability in the device and deviations due to graphite deposition on the samples, but the low temperature data should be reliable. As the specific heat data was also of poor quality, literature data was used instead. As for the thermal diffusivity data, the calculated thermal conductivity for lower temperatures are more accurate. A modified version of the porosity model by Ondracek and Schulz was used to analyse the porosity dependence of the thermal conductivity, taking into account the different impacts of open and closed porosity.

  • 3563.
    Valyukh, Sergiy
    Linköping University, Department of Physics, Chemistry and Biology, Applied Optics . Linköping University, The Institute of Technology.
    Spectrally selective flat reflective lenses for photovoltaic applications2013In: Progress In Electromagnetics Research Symposium, 2013Conference paper (Refereed)
  • 3564.
    van Breemen, Albert J. J. M.
    et al.
    Holst Centre TNO, Netherlands.
    van der Steen, Jan-Laurens
    Holst Centre TNO, Netherlands.
    van Heck, Geri
    Holst Centre TNO, Netherlands.
    Wang, Rui
    Holst Centre TNO, Netherlands; Eindhoven University of Technology, Netherlands.
    Khikhlovskyi, Vsevolod
    Holst Centre TNO, Netherlands; Eindhoven University of Technology, Netherlands.
    Kemerink, Martijn
    Eindhoven University of Technology, Eindhoven, The Netherlands.
    Gelinck, Gerwin H.
    Holst Centre TNO, Netherlands.
    Crossbar arrays of nonvolatile, rewritable polymer ferroelectric diode memories on plastic substrates2014In: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 7, no 3, article id 031602Article in journal (Refereed)
    Abstract [en]

    In this paper, we demonstrate a scalable and low-cost memory technology using a phase separated blend of a ferroelectric polymer and a semiconducting polymer as data storage medium on thin, flexible polyester foils of only 25 mu m thickness. By sandwiching this polymer blend film between rows and columns of metal electrode lines where each intersection makes up one memory cell, we obtained 1 kbit cross bar arrays with bit densities of up to 10 kbit/cm(2). (C) 2014 The Japan Society of Applied Physics

  • 3565.
    van den Berg, J. J.
    et al.
    University of Groningen, Netherlands.
    Yakimova, Rositsa
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    van Wees, B. J.
    University of Groningen, Netherlands.
    Spin transport in epitaxial graphene on the C-terminated (000(1)over-bar)-face of silicon carbide2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 1, p. 012402-Article in journal (Refereed)
    Abstract [en]

    We performed a temperature dependent study of the charge and spin transport properties of epitaxial graphene on the C-terminated (000 (1) over bar) face of silicon carbide (SiC), a system without a carbon buffer layer between the graphene and the SiC. Using spin Hanle precession in the nonlocal geometry, we measured a spin relaxation length of lambda(S) = 0.7 lm at room temperature, lower than in exfoliated graphene. We show that the charge and spin diffusion coefficient, D-C and D-S, respectively, increasingly deviate from each other during electrical measurements up to a difference of a factor 4. Thus, we show that a model of localized states that was previously used to explain D-C not equal D-S, can also be applied to epitaxial graphene systems without a carbon buffer layer. We attribute the effect to charge trap states in the interface between the graphene and the SiC. Published by AIP Publishing.

  • 3566.
    van Lith, B. S.
    et al.
    Eindhoven University of Technology - P. O. Box 513, NL-5600 MB Eindhoven, The Netherlands.
    Muntean, Adrian
    Eindhoven University of Technology - P. O. Box 513, NL-5600 MB Eindhoven, The Netherlands.
    Storm, C.
    Eindhoven University of Technology - P. O. Box 513, NL-5600 MB Eindhoven, The Netherlands.
    A continuum model for hierarchical fibril assembly2014In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 106, no 6Article in journal (Refereed)
    Abstract [en]

    Most of the biological polymers that make up our cells and tissues are hierarchically structured. For biopolymers ranging from collagen, to actin, to fibrin and amyloid fibrils this hierarchy provides vitally important versatility. The structural hierarchy must be encoded in the self-assembly process, from the earliest stages onward, in order to produce the appropriate substructures. In this letter, we explore the kinetics of multistage self-assembly processes in a model system which allows comparison to bulk probes such as light scattering. We apply our model to recent turbidimetry data on the self-assembly of collagen fibrils. Our analysis suggests a connection between diffusion-limited aggregation kinetics and fibril growth, supported by slow, power-law growth at very long time scales.

  • 3567.
    van Reenen, S.
    et al.
    Eindhoven University of Technology, Netherlands.
    Kersten, S. P.
    Eindhoven University of Technology, Netherlands.
    Wouters, S. H. W.
    Eindhoven University of Technology, Netherlands.
    Cox, M.
    Eindhoven University of Technology, Netherlands.
    Janssen, P.
    Eindhoven University of Technology, Netherlands.
    Koopmans, B.
    Eindhoven University of Technology, Netherlands.
    Bobbert, P. A.
    Eindhoven University of Technology, Netherlands.
    Kemerink, M.
    Eindhoven University of Technology, Netherlands.
    Large magnetic field effects in electrochemically doped organic light-emitting diodes2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 12, article id 125203Article in journal (Refereed)
    Abstract [en]

    Large negative magnetoconductance (MC) of similar to 12% is observed in electrochemically doped polymer light-emitting diodes at sub-band-gap bias voltages (V-bias). Simultaneously, a positive magnetoefficiency (M eta) of 9% is observed at V-bias = 2 V. At higher bias voltages, both the MC and M eta diminish while a negative magnetoelectroluminescence (MEL) appears. The negative MEL effect is rationalized by triplet-triplet annihilation that leads to delayed fluorescence, whereas the positive M eta effect is related to competition between spin mixing and exciton formation leading to an enhanced singlet: triplet ratio at nonzero magnetic field. The resultant reduction in triplet exciton density is argued to reduce detrapping of polarons in the recombination zone at low-bias voltages, explaining the observed negative MC. Regarding organic magnetoresistance, this study provides experimental data to verify existing models describing magnetic field effects in organic semiconductors, which contribute to better understanding hereof. Furthermore, we present indications of strong magnetic field effects related to interactions between trapped carriers and excitons, which specifically can be studied in electrochemically doped organic light-emitting diodes (OLEDs). Regarding light-emitting electrochemical cells (LECs), this work shows that delayed fluorescence from triplet-triplet annihilation substantially contributes to the electroluminescence and the device efficiency.

  • 3568.
    van Reenen, Stephan
    et al.
    Eindhoven University of Technology.
    Matyba, Piotr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dzwilewski, Andrzej
    Eindhoven University of Technology.
    Janssen, Rene A
    Eindhoven University of Technology.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Kemerink, Martijn
    Eindhoven University of Technology.
    Salt concentration effects in planar light-emitting electrochemical cells2011In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 21, no 10, p. 1795-1802Article in journal (Refereed)
    Abstract [en]

    Incorporation of ions in the active layer of organic semiconductor devices may lead to attractive device properties like enhanced injection and improved carrier transport. In this paper, we investigate the effect of the salt concentration on the operation of light-emitting electrochemical cells, using experiments and numerical calculations. The current density and light emission are shown to increase linearly with increasing ion concentration over a wide range of concentrations. The increasing current is accompanied by an ion redistribution, leading to a narrowing of the recombination zone. Hence, in absence of detrimental side reactions and doping-related luminescence quenching, the ion concentration should be as high as possible.

  • 3569.
    van Reenen, Stephan
    et al.
    Eindhoven University of Technology, Netherlands.
    Matyba, Piotr
    Umeå University, Sweden.
    Dzwilewski, Andrzej
    Eindhoven University of Technology, Netherlands.
    Janssen, Rene A. J.
    Eindhoven University of Technology, Netherlands.
    Edman, Ludvig
    Umeå University, Sweden.
    Kemerink, Martijn
    Eindhoven University of Technology, Netherlands.
    Salt Concentration Effects in Planar Light-Emitting Electrochemical Cells2011In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 21, no 10, p. 1795-1802Article in journal (Refereed)
    Abstract [en]

    Incorporation of ions in the active layer of organic semiconductor devices may lead to attractive device properties like enhanced injection and improved carrier transport. In this paper, we investigate the effect of the salt concentration on the operation of light-emitting electrochemical cells, using experiments and numerical calculations. The current density and light emission are shown to increase linearly with increasing ion concentration over a wide range of concentrations. The increasing current is accompanied by an ion redistribution, leading to a narrowing of the recombination zone. Hence, in absence of detrimental side reactions and doping-related luminescence quenching, the ion concentration should be as high as possible.

  • 3570.
    van Stam, Jan
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Van fraeyenhoven, Petra
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. UC Leuven Limburg, Leuven, Belgium.
    Andersén, Mikael
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Comparing Morphology in Dip-Coated and Spin-Coated Polyfluorene:Fullerene Films2016In: Proceedings of SPIE: Organic Photovoltaics XVII / [ed] Zakya H. Kafafi, Paul A. Lane, Ifor D.W. Samuel, SPIE - International Society for Optical Engineering, 2016, Vol. 9942, p. 99420D-1-99420D-10, article id UNSP 99420DConference paper (Refereed)
  • 3571.
    van Teeffelen, S.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. Kondenserade materiens teori.
    Persson, C.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. Kondenserade materiens teori.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. Teoretisk magnetism.
    Johansson, Börje
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics IV. Theoretical Magnetism. Kondenserade materiens teori.
    Doping-induced band gap narrowing in Si rich n- and p-type Si$_{1-x}$Ge$_x$2003In: Journal of Physics: Condensed Matter, Vol. 15, p. 489-Article in journal (Refereed)
  • 3572.
    Vasilakaki, M.
    et al.
    NCSR Demokritos, Inst Nanosci & Nanotechnol, Athens 15310, Greece..
    Margaris, G.
    NCSR Demokritos, Inst Nanosci & Nanotechnol, Athens 15310, Greece..
    Peddis, D.
    CNR, Ist Struttura Mat, I-00015 Monterotondo, RM, Italy..
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Yaacoub, N.
    Univ Maine, LUNAM, Inst Mol & Mat Mans, CNRS UMR 6283, F-72085 Le Mans, France..
    Fiorani, D.
    CNR, Ist Struttura Mat, I-00015 Monterotondo, RM, Italy.;Immanuel Kant Baltic Fed Univ, Ctr Nanomat Res, Kaliningrad, Russia..
    Trohidou, K.
    NCSR Demokritos, Inst Nanosci & Nanotechnol, Athens 15310, Greece..
    Monte Carlo study of the superspin glass behavior of interacting ultrasmall ferrimagnetic nanoparticles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094413Article in journal (Refereed)
    Abstract [en]

    The magnetism of a dense assembly of ultrasmall ferrimagnetic nanoparticles exhibits unique features due to the combination of intraparticle and strong interparticle interactions. To model such system we need to account for the internal particle structure and the short-and long-range interparticle interactions. We have developed a mesoscopic model for the particle assembly that includes three spins (two for the surface and one for the core) for the description of each nanoparticle, interparticle dipolar interactions and the interparticle exchange interactions for the nanoparticles in contact. The temperature dependence of the observed exchange bias effect, due to exchange coupling at the interface between core/surface spins and the interparticle exchange coupling, and the zero-field-cooled-field-cooled magnetization vs temperature curves have been investigated using the Monte Carlo simulation technique with the implementation of the Metropolis algorithm. Our simulations reproduce well the experimental data of ultrasmall similar to 2-nm MnFe2O4 nanoparticles, confirming the close relationship between the superspin glass state and the exchange-bias effect in dense nanoparticle systems, owing to the interplay between the intraparticle structure and the interparticle effects.

  • 3573.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kabashima, Yoshiyuki
    Department of Computational Intelligence and Systems Science, Tokyo Institute of Technology.
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Replica analysis of sparse l1-reconstruction with concatenated L-orthogonal basis2012In: Statistical Mechanics of Unsatisfiability and Glasses, 2012Conference paper (Refereed)
  • 3574.
    Vekilova, Olga
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Influence of stresses and impurities on thermodynamic and elastic properties of metals and alloys from ab initio theory2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Stresses and impurities may influence elastic properties, phase stability and magnetic behavior of metals and their alloys. A physical understanding of this influence is of great importance to both fundamental science and technological applications. The diverse methods used in this work allowed us to shed light on the various aspects of the problem. In particular, in this work the thermodynamic, magnetic and elastic properties of Fe and Fe-Ni alloys at Earth’s inner core conditions were investigated by means of the ab initio theory. The main features of these calculations are on one side the extreme pressure-temperature conditions; on the other side the strong-correlation effects, which at these conditions may play an unexpected role. That is why I used different approaches, ranging from molecular dynamics to the dynamical mean field theory.

    Interesting possibility for the effect of non-hydrostatic stresses on the stability of the body-centered cubic (bcc) phase of iron was observed. If detected, it could allow for an explanation of striking contradictions in high-pressure experiments. The influence of the alloying with Ni on the stability of Fe was studied. It was shown that the observed reverse of the stability trend under pressure is associated with the suppression of ferromagnetism at conditions of Earth’s inner core.

    The strong correlation effects were observed in Fe3Ni by means of the dynamical mean field theory, revealing that the local environment of iron atoms is crucial for the strength of the on-site electronic correlations.

    There is also an exciting experimental finding of our colleagues indicating that magnetism in pure nickel survives at very high pressures up to 260 GPa, i.e. up to the highest pressure at which magnetism in any material has ever been observed. Our calculations of the pressure dependence of the effective exchange interaction parameter and the hyperfine field support the picture of the ordered ferromagnetic state in Ni at multimegabar pressures.

    Further, hydrogen is believed to be an important light impurity in Earth’s core. Thereupon the hydrogen containing FeOOH was also investigated. The prediction of the effect of symmetrization of the hydrogen bond under pressure was made.

    The universality of applied methods allowed us to study the elastic constants of TiN, which is of high relevance to the industry of cutting tools. The importance of taking into account the finite temperature effects in the calculations of the elastic properties was demonstrated. Another case of practical interest is the Fe-Cr system, a prototype of many industrial steels. For instance, it is used in cooling pipes of pressure vessel reactors. We studied the effect of hydrostatic pressure on the phase stability of Fe-Cr alloys and revealed intriguing differences in the ordering tendencies depending on the Cr concentration and magnetic state of the alloy. We showed how variation of the ordering tendency between the Fe and Cr atoms emerges due to suppression of the local magnetic moment on the Cr atoms.

    Noteworthy, hydrogen is not only the basic material playing fundamental role on and in the Earth, it is also a very promising source of fuel, which does not pollute the environment. In this sense the problem of hydrogen storage in Pd is of separate but related interest and it was theoretically investigated in the present work. The effect of vacancies on the energetically preferable position of hydrogen in the Pd cell was addressed. My theoretical results supported the experimental suggestion of multiple occupation of Pd vacancies by hydrogen.

  • 3575.
    Verschueren, Daniel V
    et al.
    Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
    Jonsson, Magnus P
    Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
    Dekker, Cees
    Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands.
    Temperature dependence of DNA translocations through solid-state nanopores2015In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, p. 1-8, article id 234004Article in journal (Refereed)
    Abstract [en]

    In order to gain a better physical understanding of DNA translocations through solid-state nanopores, we study the temperature dependence of λ-DNA translocations through 10 nm diameter silicon nitride nanopores, both experimentally and theoretically. The measured ionic conductance G, the DNA-induced ionic-conductance blockades [Formula: see text] and the event frequency Γ all increase with increasing temperature while the DNA translocation time τ decreases. G and [Formula: see text] are accurately described when bulk and surface conductances of the nanopore are considered and access resistance is incorporated appropriately. Viscous drag on the untranslocated part of the DNA coil is found to dominate the temperature dependence of the translocation times and the event rate is well described by a balance between diffusion and electrophoretic motion. The good fit between modeled and measured properties of DNA translocations through solid-state nanopores in this first comprehensive temperature study, suggest that our model captures the relevant physics of the process.

  • 3576.
    Viamontes Esquivel, Alcides
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rosvall, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Compression of Flow Can Reveal Overlapping-Module Organization in Networks2011In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 1, no 2, article id 021025Article in journal (Refereed)
    Abstract [en]

    To better understand the organization of overlapping modules in large networks with respect to flow, we introduce the map equation for overlapping modules. In this information-theoretic framework, we use the correspondence between compression and regularity detection. The generalized map equation measures how well we can compress a description of flow in the network when we partition it into modules with possible overlaps. When we minimize the generalized map equation over overlapping network partitions, we detect modules that capture flow and determine which nodes at the boundaries between modules should be classified in multiple modules and to what degree. With a novel greedy-search algorithm, we find that some networks, for example, the neural network of the nematode Caenorhabditis elegans, are best described by modules dominated by hard boundaries, but that others, for example, the sparse European-roads network, have an organization of highly overlapping modules.

  • 3577. Vidal, Julien
    et al.
    Botti, Silvana
    Olsson, Pär
    Département MMC, EDF RandD, Les Renardières, France.
    Guillemoles, Jean-Francois
    Reining, Lucia
    Strong Interplay between Structure and Electronic Properties in CuIn(S, Se)(2): A First-Principles Study2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 5Article in journal (Refereed)
    Abstract [en]

    We present a first-principles study of the electronic properties of CuIn(S, Se)(2) (CIS) using state-of-the-art self-consistent GW and hybrid functionals. The calculated band gap depends strongly on the anion displacement u, an internal structural parameter that measures lattice distortion. This contrasts with the observed stability of the band gap of CIS solar panels under operating conditions, where a relatively large dispersion of values for u occurs. We solve this apparent paradox considering the coupled effect on the band gap of copper vacancies and lattice distortions. The correct treatment of d electrons in these materials requires going beyond density functional theory, and GW self-consistency is critical to evaluate the quasiparticle gap and the valence band maximum.

  • 3578. Vidya, R.
    et al.
    Ravindran, P.
    Kjekshus, A.
    Fjellvag, H.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk magnetism.
    Tailor-made electronic and magnetic properties in one-dimensional perovskite-like oxides2003In: Physical Review Letters, Vol. 91, p. 186404-Article in journal (Refereed)
    Abstract [en]

    Full-potential density-functional calculations show that the electronic structure of one-dimensional ferrimagnetic Ca3Co2O6 varies from metal to half metal to insulator as its magnetic ordering changes from the ferrimagnetic through the ferromagnetic to the paramagnetic state. The present Letter is the first to establish the occurrence of half metallicity in one-dimensional oxides. Moreover, the electronic and magnetic properties of this material can be tuned by substitution of Y for Ca, as shown by our detailed study on Ca3–xYxCo2O6 (x = 0, 0.3, 0.75, and 1). The Co ions are in two different valence states [Co4+ (low-spin) and Co2+ (high-spin)], and hence the occurrence of charge ordering in addition to spin ordering is established. For specific Y concentrations we predict a rarely seen combination of ferromagnetic and insulating behavior.

  • 3579.
    Vikström, Anton
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Curvature-Induced Energy Band Tilting in Finite-Length Carbon Nanotubes2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The near-Fermi-energy energy band structure of carbon nanotubes is given by cross-sections of the graphene Dirac cones near the K and K' points. Using second-order perturbation theory and a nearest-neighbor approximated tight-binding model, curvature-induced corrections to the graphene-based effective model are derived. In addition to the already known Dirac-point shift, the curvature is shown to cause not only a warping of the Dirac cone, tantamount to a slight compression and a correction to the overall Fermi velocity, but also a tilting of the Dirac cone and the associated nanotube energy bands. This tilting results in a velocity asymmetry for left- and right-going waves and two different kinds of excitations, allowing for varying degeneracy in the same sample. Previous experiments have shown irregularities in the level degeneracy and should be reconsidered in this context.

  • 3580.
    Vinogradov, Nikolay
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Controlling Electronic and Geometrical Structure of Honeycomb-Lattice Materials Supported on Metal Substrates: Graphene and Hexagonal Boron Nitride2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present thesis is focused on various methods of controlling electronic and geometrical structure of two-dimensional overlayers adsorbed on metal surfaces exemplified by graphene and hexagonal boron nitride (h-BN) grown on transition metal (TM) substrates. Combining synchrotron-radiation-based spectroscopic and various microscopic techniques with in situ sample preparation, we are able to trace the evolution of overlayer electronic and geometrical properties in overlayer/substrate systems, as well as changes of interfacial interaction in the latter.It is shown that hydrogen uptake by graphene/TM substrate strongly depends on the interfacial interaction between substrate and graphene, and on the geometrical structure of graphene. An energy gap opening in the electronic structure of graphene on TM substrates upon patterned adsorption of atomic species is demonstrated for the case of atomic oxygen adsorption on graphene/TM’s (≥0.35 eV for graphene/Ir(111)). A non-uniform character of adsorption in this case – patterned adsorption of atomic oxygen on graphene/Ir(111) due to the graphene height modulation is verified. A moderate oxidation of graphene/Ir(111) is found largely reversible. Contrary, oxidation of h-BN/Ir(111) results in replacing nitrogen atoms in the h-BN lattice with oxygen and irreversible formation of the B2O3 oxide-like structure.     

    Pronounced hole doping (p-doping) of graphene upon intercalation with active agents – halogens or halides – is demonstrated, the level of the doping is dependent on the agent electronegativity. Hole concentration in graphene on Ir(111) intercalated with Cl and Br/AlBr3 is as high as ~2×1013 cm-2 and ~9×1012 cm-2, respectively.    

    Unusual periodic wavy structures are reported for h-BN and graphene grown on Fe(110) surface. The h-BN monolayer on Fe(110) is periodically corrugated in a wavy fashion with an astonishing degree of long-range order, periodicity of 2.6 nm, and the corrugation amplitude of ~0.8 Å. The wavy pattern results from a strong chemical bonding between h-BN and Fe in combination with a lattice mismatch in either [11 ̅1] or [111 ̅] direction of the Fe(110) surface. Two primary orientations of h-BN on Fe(110) can be observed corresponding to the possible directions of lattice match between h-BN and Fe(110).    

    Chemical vapor deposition (CVD) formation of graphene on iron is a formidable task because of high carbon solubility in iron and pronounced reactivity of the latter, favoring iron carbide formation. However, growth of graphene on epitaxial iron films can be realized by CVD at relatively low temperatures, and the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a periodically corrugated pattern on Fe(110): it is modulated in one dimension forming long waves with a period of ~4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The novel 1D templates based on h-BN and graphene adsorbed on iron can possibly find an application in 1D nanopatterning. The possibility for growing high-quality graphene on iron substrate can be useful for the low-cost industrial-scale graphene production.

  • 3581.
    Vinogradov, Nikolay
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Simonov, Konstantin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Zakharov, Alexei
    MAX-Lab, Lund University.
    Wells, Justin
    MAX-Lab, Lund University.
    Generalov, Alexander
    Vinogradov, Alexander
    Mårtensson, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Preobrajenski, Alexei
    MAX-Lab, Lund University.
    Hole doping of graphene supported on Ir(111) by AlBr32013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 6, p. 061601-Article in journal (Refereed)
    Abstract [en]

    In this Letter we report an easy and tenable way to tune the type of charge carriers in graphene, using a buried layer of AlBr3 and its derivatives on the graphene/Ir(111) interface. Upon the deposition of AlBr3 on graphene/Ir(111) and subsequent temperature-assisted intercalation of graphene/Ir(111) with atomic Br and AlBr3, pronounced hole doping of graphene is observed. The evolution of the graphene/Br-AlBr3/Ir(111) system at different stages of intercalation has been investigated by means of microbeam low-energy electron microscopy/electron diffraction, core-level photoelectron spectroscopy and angle-resolved photoelectron spectroscopy.

  • 3582.
    Vitos, Levente
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Austenitic stainless steels from quantum mechanical calculations2004In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 6, no 4, p. 228-232Article in journal (Refereed)
    Abstract [en]

    Quantum mechanics is used to study the influence of the chemical composition on the elastic properties of austenitic stainless steels. Fe based alloys comprising approximately 15% Cr and 8% Ni are predicted to have the largest hardness among the usual austenitic steels, which, however, is associated with increased brittleness and susceptibility to various forms of localized corrosion. It is shown that few percent of additional Os or Ir to Fe15Cr8Ni alloy significantly improve on both of these shortcomings, without deteriorating the hardness.

  • 3583.
    Vitos, Levente
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Elastic property maps of austenitic stainless steels2002In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 88, no 15, p. 155501-Article in journal (Refereed)
    Abstract [en]

    The most recent advances in theory and methodology are directed towards obtaining a quantitative description of the electronic structure and physical properties of alloy steels. Specifically, we employ ab initio alloy theories to map the elastic properties of austenitic stainless steels as a function of chemical composition. The so generated data can be used in the search for new steel grades, and, as an example, we predict two basic compositions with outstanding properties among the austenitic stainless steels.

  • 3584.
    Vitos, Levente
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Evidence of large magnetostructural effects in austenitic stainless steels2006In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, no 11, p. 117210-Article in journal (Refereed)
    Abstract [en]

    The surprisingly low magnetic transition temperatures in austenitic stainless steels indicate that in these Fe-based alloys magnetic disorder might be present at room temperature. Using a first-principles approach, we have obtained a theoretical description of the stacking fault energy in Fe100-c-nCrcNin alloys as a function of composition and temperature. Comparison of our results with experimental databases provides a strong evidence for large magnetic fluctuations in these materials. We demonstrate that the effects of alloying additions on the structural properties of steels contain a dominant magnetic contribution, which stabilizes the most common austenitic steels at normal service conditions.

  • 3585.
    Vitos, Levente
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments, Materials Science and Engineering.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Stainless steel optimization from quantum mechanical calculations2003In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 2, no 1, p. 25-28Article in journal (Refereed)
  • 3586.
    Vitos, Levente
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nilsson, J. O.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Stacking fault energy and magnetism in austenitic stainless steels2008In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 77, no 6Article in journal (Refereed)
    Abstract [en]

    The stacking fault energies are used to illustrate the footprint of magnetism on the mechanical properties of Fe-Cr-Ni alloys forming the basis of austenitic stainless steels. We find that the usual chemical effects of alloying additions are accompanied by major magnetic effects, which stabilize the most common industrial alloy steels at normal service temperatures. We suggest that part of the uncertainties associated with the experimental data on the stacking fault energies are due to the strong concentration and temperature dependence originating from the persisting local magnetic moments.

  • 3587.
    Vitos, Levente
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Korzhavyi, Pavel
    KTH, Superseded Departments, Materials Science and Engineering.
    Johansson, Börje
    KTH, Superseded Departments, Materials Science and Engineering.
    Modeling of alloy steels2002In: Materials Today, ISSN 1369-7021, Vol. 5, no 10, p. 14-23Article, review/survey (Refereed)
    Abstract [en]

    The use of computational quantum mechanics for the theoretical modeling of material properties of steel was described. Steel properties depend on the microstructure formed during the manufacturing process as well as on the concentartion and distribution of alloying elements and impurities. The computational methods allows reserachers to separate the effect of alloying elements on physical and chemical properties and to map the compositional distribution into the property distribution with arbitrary accuracy. The computational material design approach based on quantum theory with thermodynamics constitutes a profound advance in the design process of industrially relevant materials.

  • 3588.
    Vitos, Levente
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Zhang, Hulei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Al-Zoubi, Noura
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Nilsson, Jan-Olof
    AB Sandvik Materials Technolgy, Sweden.
    Hertzman, Staffan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Lu, Song
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Mechanical properties and magnetism: stainless steel alloys from first-principles theory2011In: 2010 MRS Fall Meeting, 2011, p. 68-79Conference paper (Refereed)
    Abstract [en]

    Stainless steels are among the most important engineering materials, finding their principal scope in industry, specifically in cutlery, food production, storage, architecture, medical equipment, etc. Austenitic stainless steels form the largest sub-category of stainless steels having as the main building blocks the paramagnetic substitutional disordered Fe-Cr-Ni-based alloys. Because of that, austenitic steels represent the primary choice for non-magnetic engineering materials. The presence of the chemical and magnetic disorder hindered any previous attempt to calculate the fundamental electronic, structural and mechanical properties of austenitic stainless steels from first-principles theories. Our ability to reach an ab initio atomistic level approach in this exciting field has become possible by the Exact Muffin-Tin Orbitals (EMTO) method. This method, in combination with the coherent potential approximation, has proved an accurate tool in the description of the concentrated random alloys. Using the EMTO method, we presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we will discuss the role of magnetism on the stacking fault energies and elastic properties of paramagnetic Fe-based alloys.

  • 3589.
    Volkov, Anton
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Ionic and electronic transport in electrochemical and polymer based systems2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electrochemical systems, which rely on coupled phenomena of the chemical change and electricity, have been utilized for development an interface between biological systems and conventional electronics.  The development and detailed understanding of the operation mechanism of such interfaces have a great importance to many fields within life science and conventional electronics. Conducting polymer materials are extensively used as a building block in various applications due to their ability to transduce chemical signal to electrical one and vice versa. The mechanism of the coupling between the mass and charge transfer in electrochemical systems, and particularly in conductive polymer based system, is highly complex and depends on various physical and chemical properties of the materials composing the system of interest.

    The aims of this thesis have been to study electrochemical systems including conductive polymer based systems and provide knowledge for future development of the devices, which can operate with both chemical and electrical signals. Within the thesis, we studied the operation mechanism of ion bipolar junction transistor (IBJT), which have been previously utilized to modulate delivery of charged molecules. We analysed the different operation modes of IBJT and transition between them on the basis of detailed concentration and potential profiles provided by the model.

    We also performed investigation of capacitive charging in conductive PEDOT:PSS polymer electrode. We demonstrated that capacitive charging of PEDOT:PSS electrode at the cyclic voltammetry, can be understood within a modified Nernst-Planck-Poisson formalism for two phase system in terms of the coupled ion-electron diffusion and migration without invoking the assumption of any redox reactions.

    Further, we studied electronic structure and optical properties of a self-doped p-type conducting polymer, which can polymerize itself along the stem of the plants. We performed ab initio calculations for this system in undoped, polaron and bipolaron electronic states. Comparison with experimental data confirmed the formation of undoped or bipolaron states in polymer film depending on applied biases.

    Finally, we performed simulation of the reduction-oxidation reaction at microband array electrodes. We showed that faradaic current density at microband array electrodes increases due to non-linear mass transport on the microscale compared to the corresponding macroscale systems.  The studied microband array electrode was used for developing a laccase-based microband biosensor. The biosensor revealed improved analytical performance, and was utilized for in situ phenol detection.

  • 3590.
    Volkov, Anton
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Wijeratne, Kosala
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Mitraka, Evangelia
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Ail, Ujwala
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Zhao, Dan
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Tybrandt, Klas
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Wenzel Andreasen, Jens
    Technical University of Denmark, Denmark.
    Berggren, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering. Stellenbosch University, South Africa.
    Crispin, Xavier
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Zozoulenko, Igor
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, Faculty of Science & Engineering.
    Understanding the Capacitance of PEDOT:PSS2017In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 27, no 28, article id 1700329Article in journal (Refereed)
    Abstract [en]

    Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is the most studied and explored mixed ion-electron conducting polymer system. PEDOT: PSS is commonly included as an electroactive conductor in various organic devices, e.g., supercapacitors, displays, transistors, and energy-converters. In spite of its long-term use as a material for storage and transport of charges, the fundamentals of its bulk capacitance remain poorly understood. Generally, charge storage in supercapacitors is due to formation of electrical double layers or redox reactions, and it is widely accepted that PEDOT: PSS belongs to the latter category. Herein, experimental evidence and theoretical modeling results are reported that significantly depart from this commonly accepted picture. By applying a two-phase, 2D modeling approach it is demonstrated that the major contribution to the capacitance of the two-phase PEDOT: PSS originates from electrical double layers formed along the interfaces between nanoscaled PEDOT-rich and PSS-rich interconnected grains that comprises two phases of the bulk of PEDOT: PSS. This new insight paves a way for designing materials and devices, based on mixed ion-electron conductors, with improved performance.

  • 3591. Vollmer, A.
    et al.
    Ovsyannikov, R.
    Gorgoi, M.
    Krause, S.
    Oehzelt, M.
    Lindblad, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
    Mårtensson, Nils
    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.
    Karlsson, P.
    Lundvuist, M.
    Schmeiler, T.
    Pflaum, J.
    Koch, N.
    Two dimensional band structure mapping of organic single crystals using the new generation electron energy analyzer ARTOF2012In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 185, no 3-4, p. 55-60Article in journal (Refereed)
    Abstract [en]

    We report on a novel type of photoemission detector, the Angle Resolved Time Of Flight electron energy analyzer (ARTOF 10k), which enables electronic band structure determination under measurement conditions that are ideal for radiation-sensitive samples. This is facilitated through the combination of very high electron transmission and wide accessible angular range in one geometry. These properties make the ARTOF 10k predestined to investigate specimens that strongly suffer from radiation damage during photoemission experiments under "standard" conditions, such as organic single crystals, as extremely low fluxes can be used while not compromising spectra accumulation times and signal-to-noise ratio. Even though organic single crystals are of increasing fundamental and applied scientific interest, knowledge of their electronic properties is still largely based on theoretical calculations due to major experimental challenges in measuring photoemission. In this work we show that the band structures of rubrene and tetracene single crystals can be obtained with unprecedented quality using the ARTOF 10k detector. The dispersion of the highest occupied band in rubrene is confirmed in accordance with an earlier report [1] and we disclose the absence of notable dispersion for the highest occupied energy level on the surface of tetracene single crystals.

  • 3592.
    Volpati, D.
    et al.
    Durham university, UK.
    Massey, M. K.
    Durham university, UK.
    Johnson, D. W.
    Durham university, UK.
    Kotsialos, A.
    Durham university, UK.
    Qaiser, F.
    Durham university, UK.
    Pearson, C.
    Durham university, UK.
    Coleman, K. S.
    Durham university, UK.
    Tiburzi, G.
    Durham university, UK.
    Zeze, D. A.
    Durham university, UK.
    Petty, M. C.
    Durham university, UK.
    Exploring the alignment of carbon nanotubes dispersed in a liquid crystal matrix using coplanar electrodes2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 12, article id 125303Article in journal (Refereed)
    Abstract [en]

    We report on the use of a liquid crystalline host medium to align single-walled carbon nanotubes in an electric field using an in-plane electrode configuration. Electron microscopy reveals that the nanotubes orient in the field with a resulting increase in the DC conductivity in the field direction. Current versus voltage measurements on the composite show a nonlinear behavior, which was modelled by using single-carrier space-charge injection. The possibility of manipulating the conductivity pathways in the same sample by applying the electrical field in different (in-plane) directions has also been demonstrated. Raman spectroscopy indicates that there is an interaction between the nanotubes and the host liquid crystal molecules that goes beyond that of simple physical mixing.

  • 3593.
    Volpati, D.
    et al.
    UNESP Univ Estadual Paulista, Brazil.
    Spada, E. R.
    Universidade de São Paulo, Brazil .
    Pla Cid, C. C.
    Universidade Federal de Santa Catarina, Brazil .
    Sartorelli, M. L.
    Universidade Federal de Santa Catarina, Brazil .
    Aroca, R. F.
    University of Windsor, Canada .
    Constantino, C. J. L.
    UNESP Univ Estadual Paulista, Brazil.
    Exploring copper nanostructures as highly uniform and reproducible substrates for plasmon-enhanced fluorescence2015In: The Analyst, ISSN 0003-2654, E-ISSN 1364-5528, Vol. 140, no 2, p. 476-482Article in journal (Refereed)
    Abstract [en]

    The unique properties of metallic nanostructures of coinage metals that can sustain localized surface plasmon resonances (LSPR) put them at the centre of plasmon-enhanced phenomena. The theory of plasmonic phenomena based on LSPR is well-established. However, the fabrication of plasmonic substrates, reproducibly, is still challenging for applications in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). In this work we describe well-ordered copper nanostructures (CuNSs), produced by electrodeposition and nanosphere lithography, as active substrates for SEF. After a detailed spectroscopic and microscopic characterization, CuNSs are successfully applied as SEF-active substrates using a well-known perylene derivative as a target molecule. The signal reproducibility from CuNS substrates was established by comparing the results against those obtained from a simply roughened Cu substrate. Under optimal conditions, signal variability is around 4%.

  • 3594.
    Volpati, Diogo
    et al.
    University of São Paulo, Brazil.
    Aoki, Pedro H. B.
    UNESP, Brazil.
    Alessio, Priscila
    UNESP, Brazil.
    Pavinatto, Felippe J.
    University of São Paulo, Brazil.
    Miranda, Paulo B.
    University of São Paulo, Brazil.
    Constantino, Carlos J. L.
    UNESP, Brazil.
    Oliveira, Osvaldo N., Jr.
    University of São Paulo, Brazil.
    Vibrational spectroscopy for probing molecular-level interactions in organic films mimicking biointerfaces2014In: Advances in Colloid and Interface Science, ISSN 0001-8686, E-ISSN 1873-3727, Vol. 207, no Special Issue: Helmuth Möhwald Honorary Issue, p. 199-215Article in journal (Refereed)
    Abstract [en]

    Investigation into nanostructured organic films has served many purposes, including the design of functionalized surfaces that may be applied in biomedical devices and tissue engineering and for studying physiological processes depending on the interaction with cell membranes. Of particular relevance are Langmuir monolayers, Langmuir-Blodgett (LB) and layer-by-layer (LbL) films used to simulate biological interfaces. In this review, we shall focus on the use of vibrational spectroscopy methods to probe molecular-level interactions at biomimetic interfaces, with special emphasis on three surface-specific techniques, namely sum frequency generation (SFG), polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and surface-enhanced Raman scattering (SERS). The two types of systems selected for exemplifying the potential of the methods are the cell membrane models and the functionalized surfaces with biomolecules. Examples will be given on how SFG and PM-IRRAS can be combined to determine the effects from biomolecules on cell membrane models, which include determination of the orientation and preservation of secondary structure. Crucial information for the action of biomolecules on model membranes has also been obtained with PM-IRRAS, as is the case of chitosan removing proteins from the membrane. SERS will be shown as promising for enabling detection limits down to the single-molecule level. The strengths and limitations of these methods will also be discussed, in addition to the prospects for the near future.

  • 3595.
    Volpati, Diogo
    et al.
    University of São Paulo, Brazil.
    Chachaj-Brekiesz, Anna
    Jagiellonian University, Poland.
    Souza, Adriano L.
    University of São Paulo, Brazil.
    Rimoli, Caio Vaz
    University of São Paulo, Brazil.
    Miranda, Paulo B.
    University of São Paulo, Brazil.
    Oliveira, Osvaldo N., Jr.
    University of São Paulo, Brazil.
    Dynarowicz-Latka, Patrycja
    Jagiellonian University, Poland.
    Semifluorinated thiols in Langmuir monolayers: A study by nonlinear and linear vibrational spectroscopies2015In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 460, p. 290-302Article in journal (Refereed)
    Abstract [en]

    A series of semifluorinated thiols of the general formula CmF2m+1CnH2nSH (abbr. FmHnSH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F-10) and variable length of the hydrogenated part (H-6, H-10, H-12), and having identical hydrogenated segment (H-12) connected to a fluorinated moiety of different lengths (F-6, F-8, F10). For the sake of comparison, an alkanethiol (H18SH) was also examined, and F10H10COOH and F10H10OH molecules were used for helping the assignment of SFG spectra of CH stretches. SFG was applied to investigate the hydrocarbon chain and the terminal CF3 group, while PM-IRRAS was used to probe CF2 groups. The number of gauche defects in the hydrocarbon chain increased with the increasing length of the molecule, either by elongation of the hydrogenated or perflu-orinated part. SFG measurements recorded at three polarization combinations (ppp, ssp, sps) enabled us to estimate the tilt angle of the terminal CF3 group in semifluorinated thiol molecules as ranging from 35 to 45, which is consistent with nearly vertical fluorinated segments. Upon increasing the surface pressure, the fluorinated segment gets slightly more upright, but the hydrocarbon chain tilt increases while keeping the same average number of gauche defects. The extent of disorder in the hydrogenated segment may be controlled by varying the size of the fluorinated segment, and this could be exploited for designing functionalized surfaces with insertion of other molecules in the defect region.

  • 3596.
    Volpi, Riccardo
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, Faculty of Science & Engineering.
    Modelling Charge Transport for Organic Solar Cells within Marcus Theory2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    With the technological advancement of modern society, electronic devices are getting progressively more integrated in our everyday lives. Their continuouslygrowing presence is generating numerous concerns about costs, efficiency and the environmental impact of the electronic waste. In this context, organic electronics is finding its way through the market, allowing for potentially low-cost, light, flexible, transparent and environmentally friendly electronics. Despite the numerous successes of organic electronics, the functioning of several categories of organic devices still represents a technological challenge, due to problems like low efficiencies and stabilities (degradation over time).

    Organic devices are composed by one or more organic materials depending on the particular application. The conformation and electronic structure of the organic molecules as well as their supramolecular arrangement in the single phase or at the interface are known to strongly a affect the mobility and/or the efficiency of the device. While there is consensus on the fundamental physics of organic devices, we still lack a detailed comprehensive theory able to fully explain experimental data. In this thesis we focus on trying to expand our knowledge of charge transport in organic materials through theoretical modelling and simulation of organic electronic devices. While the methodology developed is generally valid for any organic device, we will particularly focus on the case represented by organic photovoltaics.

    The morphology of the system is obtained by molecular dynamics simulations. Marcus theory is used to calculate the hopping rate of the charge carriers and subsequently study the possibility of free charge carriers production in an organic solar cell. The theory is then compared both with Kinetic Monte Carlo simulations and with experiments to identify the main pitfalls of the actual theory and ways to improve it. The Marcus rate between two molecules depends on the molecular orbital energies, the transfer integral between the two molecules and the reorganization energy. The orbital energies and the transfer integrals between two neighbouring molecules are obtained through quantum mechanical calculations in vacuum. Electrostatic effects of the environment are included through atomic charges and atomic polarizabilities, producing a correction both to the orbital energy and to the reorganization energy. We have studied several systems in the single phase (polyphenylene vinylene, C60, PC61BM) and at the interface between two organic materials (anthracene/C60, TQ1/PC71BM).

    We show how a combination of different methodologies can be used to obtain a realistic ab-initio model of organic devices taking into account environmental effects. This allows us to obtain qualitative agreement with experimental data of mobility in the single phase and to determine whether or not two materials are suitable to be used together in an organic solar cell.

  • 3597.
    Volpi, Riccardo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
    Nassau, Racine
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Nörby, Morten
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. University of Southern Denmark, Denmark.
    Linares, Mathieu
    Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
    Theoretical Study of the Charge-Transfer State Separation within Marcus Theory: The C-60-Anthracene Case Study2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 37, p. 24722-24736Article in journal (Refereed)
    Abstract [en]

    We study, within Marcus theory, the possibility of the charge-transfer (CT) state splitting at organic interfaces and a subsequent transport of the free charge carriers to the electrodes. As a case study we analyze model anthracene-C-60 interfaces. Kinetic Monte Carlo (KMC) simulations on the cold CT state were performed at a range of applied electric fields, and with the fields applied at a range of angles to the interface to simulate the action of the electric field in a bulk heterojunction (BHJ) interface. The results show that the inclusion of polarization in our model increases CT state dissociation and charge collection. The effect of the electric field on CT state splitting and free charge carrier conduction is analyzed in detail with and without polarization. Also, depending on the relative orientation of the anthracene and C-60 molecules at the interface, CT state splitting shows different behavior with respect to both applied field strength and applied field angle. The importance of the hot CT in helping the charge carrier dissociation is also analyzed in our scheme.

  • 3598.
    von Hofsten, Olof
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Bertilson, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Vogt, Ulrich
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Theoretical development of a high-resolution differential-interference-contrast optic for x-ray microscopy2008In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, no 2, p. 1132-1141Article in journal (Refereed)
    Abstract [en]

    In this paper, the theoretical background and development of a differential-interference contrast (DIC) x-ray optic is presented. The single-element optic is capable of high-resolution phase contrast imaging and is compatible with compact sources. It is shown that an understanding of the coherence requirements in this type of imaging is imperative and is explained in detail. The optic is capable of a wavefront separation equal to the resolution of the optic which places only minor constraints on the object illumination.

  • 3599. Vorobiev, Alexei
    et al.
    Dennison, Andrew
    Chernyshov, Dmitry
    Skyrpnychuck, Vasyl
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Barbero, David
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Talyzin, Alexandr
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Graphene oxide hydration and solvation: an in situ neutron reflectivity study2014In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, no 20, p. 12151-12156Article in journal (Refereed)
    Abstract [en]

    Graphene oxide membranes were recently suggested for applications in separation of ethanol from water using a vapor permeation method. Using isotope contrast, neutron reflectivity was applied to evaluate the amounts of solvents intercalated into a membrane from pure and binary vapors and to evaluate the selectivity of the membrane permeation. Particularly, the effect of D2O, ethanol and D2O–ethanol vapours on graphene oxide (GO) thin films (25 nm) was studied. The interlayer spacing of GO and the amount of intercalated solvents were evaluated simultaneously as a function of vapour exposure duration. The significant difference in neutron scattering length density between D2O and ethanol allows distinguishing insertion of each component of the binary mixture into the GO structure. The amount of intercalated solvent at saturation corresponds to 1.4 molecules per formula unit for pure D2O (1.4 monolayers) and 0.45 molecules per formula unit (one monolayer) for pure ethanol. This amount is in addition to H2O absorbed at ambient humidity. Exposure of the GO film to ethanol–D2O vapours results in intercalation of GO with both solvents even for high ethanol concentration. A mixed D2O–ethanol layer inserted into the GO structure is water enriched compared to the composition of vapours due to slower ethanol diffusion into GO interlayers

  • 3600.
    Vorona, Igor
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Buyanova, Irina
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Chen, Weimin
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Utsumi, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Furukawa, Y.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Moon, S.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Wakahara, A.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Yonezu, H.
    Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, Japan.
    Intrinsic paramagnetic defects in GaNP alloys grown on silicon2006In: 210th ECS Meeting Volume 3, Issue 5: State-of-the-Art Program on Compound Semiconductors 45 (SOTAPOCS 45) -and- Wide Bandgap Semiconductor Materials and Devices 7 / [ed] F. Ren, J. Bardwell, P. Chang, W. Johnson, P. Shen, E. Stokes, Electrochemical Society, 2006, Vol. 3, p. 231-236Conference paper (Other academic)
    Abstract [en]

    Wepresent our recent results of grown-in defects in the GaNPalloy lattice matched to Si, by optically detected magnetic resonance.One of the defects was identified as the Gai-B complex,commonly formed in dilute nitrides. The remaining defects are suggestedto be probably related to intrinsic defects as well.

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