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  • 1.
    Andersson, Mattias
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Jakobsson, Fredrik L.E.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Berggren, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lindgren, L.
    Polymer Chemistry, Department of Materials and Surface Chemistry, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
    Andersson, M.R.
    Polymer Chemistry, Department of Materials and Surface Chemistry, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
    Inganäs, Olle
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics.
    Intrinsic and extrinsic influences on the temperature dependence of mobility in conjugated polymers2008In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 9, no 5, 569-574 p.Article in journal (Refereed)
    Abstract [en]

    The temperature dependence of charge carrier mobility in conjugated polymers and their blends with fullerenes is investigated with different electrical methods, through field effect transistor (FET), space charge limited current (SCLC) and charge extraction (CELIV) measurements. Simple models, such as the Gaussian disorder model (GDM), are shown to accurately predict the temperature behavior, and a good correlation between the different measurement methods is obtained. Inconsistent charge carrier concentrations in the modeling are explained through intrinsic non-equilibrium effects, and are responsible for the limited applicability of existing numerical models. A severe extrinsic influence from water in FETs with a hydrophilic insulator interface is also demonstrated. The presence of water leads to a significant overestimate of the disorder in the materials from measurements close to room temperature and erratic behavior in the 150-350 K range. To circumvent this problem it is shown to be necessary to measure under ultra high vacuum (UHV) conditions. © 2008 Elsevier B.V. All rights reserved.

  • 2.
    Braun, Slawomir
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, M.P.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Influence of the electrode work function on the energy level alignment at organic-organic interfaces2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 20Article in journal (Refereed)
    Abstract [en]

    The energy level alignment at interfaces, in stacks comprising of (4, 4′ -N, N′ -dicarbazolyl-biphenyl) (CBP), (4,4, 4″ -tris[3-methyl-phenyl(phenyl)amino]-triphenylamine) (m -MTDATA), and a conductive substrate, has been studied. We show that the alignment of energy levels depends on the equilibration of the chemical potential throughout the layer stack, while any electronic coupling between the individual layers is of lesser importance. This behavior is expected to occur for a broad class of weakly interacting interfaces and can have profound consequences for the design of organic electronic devices. © 2007 American Institute of Physics.

  • 3.
    Braun, Slawomir
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Wang, Ying
    E. I. DuPont de Nemours and Co., Inc., Experimental Station, Wilmington, DE, United States.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Energy level alignment regimes at hybrid organic–organic and inorganic–organic interfaces2007In: Organic Electronics, ISSN 1566-1199, Vol. 8, no 1, 14-20 p.Article in journal (Refereed)
    Abstract [en]

    Ultraviolet photoelectron spectroscopy has been used to determine the energy level alignment at interfaces of molecular hole-transporting materials and various conductive substrates. Depending on the work function of the substrate, s, a transition between two different energy level alignment regimes has been observed: namely vacuum level alignment and Fermi level pinning. The transition is associated with spontaneous positive charge transfer across the interface to the organic semiconductors above a certain material-specific threshold value of s. The charge transfer results in formation of an interfacial dipole of a magnitude that scales with s. In the vacuum level alignment regime, the hole-injection barriers scale linearly with s, while in the Fermi level pinning regime, these barriers are constant and independent of s.

  • 4.
    Crispin, Xavier
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Marciniak, S.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Zotti, G.
    Instituto Consiglio Nazionale delle Ricerche per l' Energetica e le Interfasi, Padova, Italy.
    Denier Van Der Gon, A. W.
    Faculty of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
    Louwet, F.
    Chemistry Department, R&D Materials Research, Agfa Gevaert N.V., Mortsel, Belgium.
    Fahlman, Mats
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Groenendaal, L.
    Chemistry Department, R&D Materials Research, Agfa Gevaert N.V., Mortsel, Belgium.
    De Schryver, F.
    Afdeling Fotochemie en Spectroscopie, Katholieke Universiteit Leuven, Heverlee, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Conductivity, Morphology, Interfacial Chemistry, and Stability of Poly(3,4- ethylene dioxythiophene)–Poly(styrene sulfonate): A Photoelectron Spectroscopy Study2003In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 41, no 21, 2561-2583 p.Article, review/survey (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) has been used to characterize poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDT/PSS), one of the most common electrically conducting organic polymers. A correlation has been established between the composition, morphology, and polymerization mechanism, on the one hand, and the electric conductivity of PEDT/PSS, on the other hand. XPS has been used to identify interfacial reactions occurring at the polymer-on-ITO and polymer-on-glass interfaces, as well as chemical changes within the polymer blend induced by electrical stress and exposure to ultraviolet light.

  • 5. da Silva, DA
    et al.
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Coropceanu, V
    Ohrwall, G
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Suess, C
    Sorensen, SL
    Svensson, S
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Bredas, JL
    Vibronic coupling in the ground and excited states of the naphthalene cation2004In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 15, 1702-1703 p.Article in journal (Refereed)
    Abstract [en]

    The hole - vibrational coupling in naphthalene is studied using high-resolution gas-phase photoelectron spectroscopy and density functional theory calculations (DFT), and a remarkable increase of the coupling with low-frequency vibrations is observed in the excited states.

  • 6. De Cupere, V.
    et al.
    Tant, J.
    Viville, P.
    Lazzaroni, R.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Geerts, Y. H.
    Effect of interfaces on the alignment of a discotic liquid-crystalline phthalocyanine2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 18, 7798-7806 p.Article in journal (Refereed)
    Abstract [en]

    This paper deals with the influence of the nature and number of solid interfaces on the alignment of the columns in a semiconducting discotic liquid crystal. The solid substrates have been characterized in terms of their roughness and surface energy. The alignment of the discotic liquid crystal columns on these substrates has been determined by optical microscopy under crossed polarizers and by tapping-mode atomic force microscopy. The nature of the substrates has negligible influence on the alignment. The key parameter is the confinement imposed to the film. These surprising observations are explained by the antagonist alignment role of gas and solid interfaces. © 2006 American Chemical Society.

  • 7.
    de Jong, Michel P
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Bergenti, I.
    ISMN-CNR, via Gobetti 101, 40129 Bologna, Italy.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Dediu, V.A.
    ISMN-CNR, via Gobetti 101, 40129 Bologna, Italy.
    Taliani, C.
    ISMN-CNR, via Gobetti 101, 40129 Bologna, Italy.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Valence electronic states related to Mn2+ at La0.7 Sr0.3 MnO3 surfaces characterized by resonant photoemission2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 5Article in journal (Refereed)
    Abstract [en]

    Nonferromagnetic Mn2+ ions can be readily formed at the surface of half metallic La0.7 Sr0.3 MnO3 manganite as demonstrated by deoxygenating surface treatments. The 3 d5 contribution of these Mn2+ ions to the valence-band electronic structure has been characterized using Mn(2p) to 3d resonant photoemission measurements. The Mn2+ related 3d electrons were found to be stabilized by about 2 eV with respect to the mixed-valence 3d states, indicating their strong localization. Active participation of Mn2+ states in both spin and charge conductivity processes is therefore excluded. A two-channel picture, including independent Mn3+ Mn4+ and Mn2+ channels, emerges from detailed data analysis. Reversible Mn2+ formation and straightforward oxygen annealing effects point to a direct bonding between Mn2+ and oxygen vacancies that are most probably created at preexisting structural defects. The t2g and eg states of the mixed valence Mn3+ Mn4+ ions remain unaffected as the Mn2+ content increases, indicating a robust Mn3+ Mn4+ channel independent of structural defects. © 2006 The American Physical Society.

  • 8.
    de Jong, Michel P
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Ultraviolet photoelectron spectroscopy of polymers2006In: MOLECULAR CRYSTALS AND LIQUID CRYSTALS, ISSN 1542-1406, Vol. 455, 193-203 p.Article in journal (Refereed)
    Abstract [en]

    During the past three decades, ultraviolet photoelectron spectroscopy of polymer films has evolved from a sort of appearance-potential ( valence band edge) measurement, into a tool for studying the full valence band region of thin polymer films, including insulating polymers, semiconducting polymers and electrically conducting polymers. Progress may be loosely divided into several categories: (A) the melding of thin polymer film technology with ultra high vacuum technology and the widespread use of helium resonance lamps for studies of solid surfaces, (B) the combined approach of measurements and appropriate theoretical-computational methods, and (C) the advent of synchrotron radiation resulting in multi-photon spectroscopies, nominally in the area of the near UV. A coincident discovery of electrically conducting polymers, and especially the evolution of applications of semiconducting polymers, added technologically driven emphasis to this development of UPS for polymer materials. This contribution traces a limited number of highlights in the evolution of UPS of polymers, from the '70' s through to 2005.

  • 9.
    de Jong, Michel P
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Friedlein, Rainer
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Sorensen, S. L.
    Department of Synchrotron Radiation Research, Institute of Physics, University of Lund, Lund, Sweden.
    Öhrwall, G.
    Department of Physics, Uppsala University, Uppsala, Sweden.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Tengstedt, Carl
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Jönsson, Stina
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Orbital-specific dynamic charge transfer from Fe(II)-tetraphenylporphyrin molecules to molybdenum disulfide substrates2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 3, 35448- p.Article in journal (Refereed)
    Abstract [en]

    Orbital-specific femtosecond charge transfer dynamics between Fe(II)-tetraphenylporphyrin molecules and semimetallic molybdenum disulfide substrates is investigated using core-level resonant photoemission spectroscopy. The electronic coupling to the substrate and the efficiency of charge transport across the interface is found to be different for the individual molecular electronic subsystems. In particular, electrons excited at the phenyl substituents are transferred within 3–6 fs, while hopping from the porphyrin ring is slower than 30 fs.

  • 10.
    de Jong, Michel P
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Sorensen, S.L.
    Department of Synchrotron Radiation Research, Lund University, Box 118, 221 00 Lund, Sweden.
    Sergeyev, S.
    Laboratory of Polymer Chemistry, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Bruxelles, Belgium.
    Geerts, Y.H.
    Laboratory of Polymer Chemistry, Université Libre de Bruxelles, Boulevard du Triomphe, 1050 Bruxelles, Belgium.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Femtosecond charge transfer in assemblies of discotic liquid crystals2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 40, 15784-15790 p.Article in journal (Refereed)
    Abstract [en]

    The electronic coupling strength within columns of discotic liquid crystals is investigated using core-level resonant photoemission spectroscopy. Coexisting well-ordered and disordered regions are identified in thin films of tetra-alkoxy-substituted phthalocyanines with the aid of near edge X-ray absorption fine structure and photoelectron spectroscopies. These different regions are used to derive a lower limit for the intermolecular charge transfer bandwidth within the framework of the core-hole clock principle. We find average charge transfer times on the order of a few femtoseconds, that is, significantly faster than the C(ls) core-hole lifetime, which indicates a surprisingly strong electronic coupling between the phthalocyanine units as compared to what is expected from the charge transport characteristics of this material. © 2008 American Chemical Society.

  • 11.
    de Jong, Michel P
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Van, Der Gon A.W.D.
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Groenendaal, L.
    Agfa-Gevaert N.V., R and D Materials - Chemistry Dept., Septestraat 27, B-2640 Mortsel, Belgium.
    The electronic structure of n- and p-doped phenyl-capped 3,4-ethylenedioxythiophene trimer2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 118, no 14, 6495-6502 p.Article in journal (Refereed)
    Abstract [en]

    A study was conducted on the effects of chemical doping on the chemical and electronic structure of condensed molecular solid films of the ethylenedioxythiophene (EDOT) trimer using ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). Phenyl-capped EDOT oligomers were potential candidates for molecular electronics applications and serve as model molecules for PEDOT. By combining UPS, XPS, and NEXAFS, a clear picture of the doping induced changes in the electronic structure of phenyl-capped EDOT-trimer was obtained.

  • 12.
    Fahlman, Mats
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Henze, S.K.M.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Tengstedt, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of hybrid interfaces for polymer-based electronics2007In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 19, no 18Article, review/survey (Refereed)
    Abstract [en]

    The fundamentals of the energy level alignment at anode and cathode electrodes in organic electronics are described. We focus on two different models that treat weakly interacting organic/metal (and organic/organic) interfaces: the induced density of interfacial states model and the so-called integer charge transfer model. The two models are compared and evaluated, mainly using photoelectron spectroscopy data of the energy level alignment of conjugated polymers and molecules at various organic/metal and organic/organic interfaces. We show that two different alignment regimes are generally observed: (i) vacuum level alignment, which corresponds to the lack of vacuum level offsets (Schottky-Mott limit) and hence the lack of charge transfer across the interface, and (ii) Fermi level pinning where the resulting work function of an organic/metal and organic/organic bilayer is independent of the substrate work function and an interface dipole is formed due to charge transfer across the interface. We argue that the experimental results are best described by the integer charge transfer model which predicts the vacuum level alignment when the substrate work function is above the positive charge transfer level and below the negative charge transfer level of the conjugated material. The model further predicts Fermi level pinning to the positive (negative) charge transfer level when the substrate work function is below (above) the positive (negative) charge transfer level. The nature of the integer charge transfer levels depend on the materials system: for conjugated large molecules and polymers, the integer charge transfer states are polarons or bipolarons, for small molecules' highest occupied and lowest unoccupied molecular orbitals and for crystalline systems, the relevant levels are the valence and conduction band edges. Finally, limits and further improvements to the integer charge transfer model are discussed as well as the impact on device design. © IOP Publishing Ltd.

  • 13.
    Fahlman, Mats
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Sehati, Parisa
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Braun, Slawomir
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    de Jong, Michel P.
    University of Twente, Netherlands .
    Brocks, Geert
    University of Twente, Netherlands University of Twente, Netherlands .
    Photoelectron spectroscopy and modeling of interface properties related to organic photovoltaic cells2013In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 190, 33-41 p.Article in journal (Refereed)
    Abstract [en]

    In this short review, we will give examples on how photoelectron spectroscopy (PES) assisted by models on interface energetics can be used to study properties important to bulk heterojunction type organic photovoltaic devices focusing on the well-known bulk heterojunction blend of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) and its model system P3HT:C-60. We also will discuss some of the limitations of PES as applied to organic semiconductors (OS) and photovoltaic devices and finish with reviewing recent theoretical advances that now enable calculation of relevant parameters at (hybrid) interfaces measured by PES.

  • 14.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Braun, Slawomir
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Simpson, CD
    Watson, MD
    von Kieseritzky, F
    Samori, P
    Jonsson, SKM
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Jackel, F
    Rabe, JP
    Hellberg, J
    Mullen, K
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Surface-induced vertical alignment of self-assembled supramolecular columns of large polycyclic aromatic hydrocarbons and porphyrins2004In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 147, no 01-Mar, 79-83 p.Article in journal (Refereed)
    Abstract [en]

    Ordered films of polycyclic aromatic hydrocarbons (PAHs) and porphyrins with functional (e.g. thiophene) side-groups are good candidates for (opto-)electronic applications where fast charge separation and transport are required. Such highly ordered thin films of PAHs, including discotic hexa-peri-hexabenzocoronene (HBC) and C-132-C-16,C-4, as well as brominated functionalized porphyrin molecules have been grown from solutions on semi-metallic molybdenum disulfide substrates and characterized by angle-resolved valence band photoelectron spectroscopy. A vertical growth of self-assembled supramolecular columns perpendicular to the basal plane of the substrate along with their lateral ordering on the surface has been achieved. Annealing made it possible to increase the structural order in the HBC columns, with molecules positioned at a regular offset from the columnar axis. This permitted the formation of extended pi-electronic states with a bandwidth of at least 0.1-0.2 eV at room temperature. (C) 2004 Elsevier B.V. All rights reserved.

  • 15.
    Friedlein, Rainer
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Simpson, C. D.
    Max Planck Institute for Polymer Research, Germany.
    Watson, M. D.
    Max Planck Institute for Polymer Research, Germany.
    Jackel, F.
    Department of Physics, Humboldt University Berlin, Berlin, Germany.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Marciniak, S.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    de Jong, Michel P
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Samori, P.
    Department of Physics, Humboldt University Berlin, Berlin, Germany.
    Jönsson, Stina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Müllen, K.
    Max Planck Institute for Polymer Research, Germany.
    Rabe, J. P.
    Department of Physics, Humboldt University Berlin, Berlin, Germany.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Electronic structure of highly ordered films of self-assembled graphitic nanocolumns2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 19, 195414- p.Article in journal (Refereed)
    Abstract [en]

    Highly ordered, several nanometers thick films of alkylated large planar, polycyclic aromatic hydrocarbon (PAH) molecules have been grown on semi-metallic molybdenum disulfide substrates. The films are characterized by a two-dimensional lateral arrangement of columns standing at the surface on a macroscopic scale. The self-assembly of such insulated columns of face-to-face disks with surface-induced vertical alignment has been achieved directly from solution processing. Angle-resolved photoelectron spectra revealed a highly anisotropic quasi-one-dimensional electronic structure with an extended π-electronic wave function. An intermolecular dispersion of the highest occupied band of at least 0.15 eV along the stacking direction has been measured. A partial breakdown of the concept of quasimomentum due to the finite size of the nano-objects perpendicular to the stacks is observed.

  • 16.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Sorensen, SL
    Baev, A
    Gel'mukhanov, F
    Birgerson, J
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Murphy, C
    Agren, H
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Role of electronic localization and charge-vibrational coupling in resonant photoelectron spectra of polymers: Application to poly(para-phenylenevinylene)2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 12Article in journal (Refereed)
    Abstract [en]

    A combination of x-ray absorption and resonant photoemission (RPE) spectroscopy has been used to study the electronic structure of the one-dimensional conjugated polymer poly (para-phenylenevinylene) in nonordered (as prepared) thin films. The dispersion of RPE features for the decay to localized and delocalized bands are qualitatively different. A theory for band dispersion of RPE in polymers is given, showing the important roles of electronic state localization and vibrational (phonon) excitations for the character of the dispersion.

  • 17.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Sorensen, S.L.
    Sörensen, S.L., Department of Synchrotron Radiation Research, Institute of Physics, Lund University, S-221 00 Lund, Sweden.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Rosenqvist, L.
    Department of Synchrotron Radiation Research, Institute of Physics, Lund University, S-221 00 Lund, Sweden.
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Murphy, C.
    CDT Ltd., Cambridge CB3 0KJ, United Kingdom.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of conjugated polymers and interfaces in polymer-based electronics2003Conference paper (Refereed)
    Abstract [en]

    The electronic structure of conjugated polymers and interfaces in polymer-based electronics were analyzed. Fine structure were observed in the region of the first resonance with pi-final state symmetry, between 284.1 eV and 285.8 eV. The electronic transitions from the non-dispersed C(1s) level to specific parts of the unoccupied band structure were generated. It was found that for a dispersing valence band, in the presence of a core-hole, a given photon energy corresponded to an excitation into a state with a distinct wave vectors.

  • 18.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    von Kieseritzky, Fredrik
    Braun, Slawomir
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Linde, Christian
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Hellberg, Jonas
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Solution-processed, highly-oriented supramolecular architectures of functionalized porphyrins with extended electronic states2005Article in journal (Refereed)
    Abstract [en]

    Thin films of aligned supramolecular architectures built from newly synthesized thiophene-substituted porphyrins have been processed from solution on surfaces. © The Royal Society of Chemistry 2005.

  • 19. Greczynski, G.
    et al.
    Kugler, Th.
    ACREO AB, Interconnect and Packaging, Bredgatan 34, S-602 21 Norrköping, Sweden.
    Keil, M.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Photoelectron spectroscopy of thin films of PEDOT-PSS conjugated polymer blend: A mini-review and some new results2001In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 121, no 1-3Article, review/survey (Refereed)
    Abstract [en]

    We present an overview of the photoelectron spectroscopy studies of thin films of the commercially important, electrically conducting polymer blend poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate), PEDOT-PSS. The issues discussed include the study of thermal effects, the influence of hydrochloric acid on the chemical and electronic structures of the films, phase segregation, as well as the energy level alignment at interfaces employing a PEDOT-PSS layer. All of these issues are important in applications of PEDOT-PSS as a hole-injecting electrode in polymer-based, light-emitting devices. Among the most important results are the identification of the three chemically different species in pristine PEDOT-PSS, namely poly(4-styrenesulfonic acid), poly(sodium 4-styrenesulfonate) and poly(3,4-ethylenedioxythiophene), the conversion of the sodium salt into free poly(styrenesulfonic acid) upon HCl treatment, and the decomposition of the free sulfonic acid component (presumably through loss of SO3H) induced by annealing. It is also shown that phase segregation occurs in the PEDOT-PSS system, resulting in a predominance of PSS in the surface region. This issue has been studied using different approaches, including X-ray photoelectron spectroscopy studies of the sulfur S(2p) and oxygen O(1s) core levels, ultraviolet photoelectron spectroscopy of the valence band region combined with reference measurements and quantum chemical calculations, as well as variable photon energy investigations of sulfur S(2p) core levels. It is demonstrated that, in the context of the energy level alignment at the polymer-metal interfaces, PEDOT-PSS shows metallic-like behavior. Due to the latter, the insertion of a thin PEDOT-PSS layer between the hole-injecting electrode ITO and a polymer layer of poly(bis-(2-dimethyloctylsilyl)-1,4-phenylenevinylene) leads to the lowering of the barrier for hole injection, independent of the work function of the underlying ITO. PEDOT-PSS is also used to show the alignment of the electrochemical potential across metal-polymer-metal structures. © 2001 Elsevier Science B.V. All rights reserved.

  • 20.
    Jönsson, Stina
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Birgerson, J.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Denier van der Gon, A.W.
    Denier van der Gon, A.W., Faculty of Applied Physics, Eindhoven University of Technology, Eindhoven, Netherlands.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    The effects of solvents on the morphology and sheet resistance in poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS) films2003In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 139, no 1, 1-10 p.Article in journal (Refereed)
    Abstract [en]

    Films of poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS), prepared by coating the aqueous PEDOT–PSS dispersion and by coating a mixture of the PEDOT–PSS dispersion and different solvents, have been studied using four-point probe conductivity measurements, atomic force microscopy and photoelectron spectroscopy. The electrical conductivity of thin films of the second type (further on called PEDOT–PSS–solvents) was increased by a factor of about 600 as compared to films of the first type (further on called PEDOT–PSS–pristine). Morphological and physical changes occur in the polymer film due to the presence of the solvent mixture, the most striking being that the ratio of PEDOT-to-PSS in the surface region of the films is increased by a factor of ∼2–3. This increase of PEDOT at the surface indicates that the thickness of the insulating PSS ‘shell’ that surrounds the conducting PEDOT–PSS grains is reduced. The (partial) reduction of the excess PSS layer that surrounds the conducting PEDOT–PSS grains is proposed to lead to an increased and improved connectivity between such grains in the film and hence a higher conductivity. When PEDOT–PSS–solvents receives a post-coating heat treatment, the increased PEDOT-to-PSS ratio at the surface is maintained or even slightly improved, as is the increase in electrical conductivity, even though spectroscopy show that the solvent molecules are removed. This suggests that screening or doping by the solvents throughout the film are not likely to be the key mechanisms for the improved conductivity and supports our proposed mechanism of improved conductivity through improved connectivity between the conducting grains.

  • 21.
    Lindell, Linda
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Lazzaroni, R
    Berggren, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Characterization of the interface dipole at the paraphenylenediamine-nickel interface: A joint theoretical and experimental study2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 8, 84712- p.Article in journal (Refereed)
    Abstract [en]

    In organic-based (opto)electronic devices, charge injection into conjugated materials is governed to a large extent by the metal-organic interface dipole. Controlling the injection of charges requires a better understanding of the fundamental origin of the interface dipole. In this context, photoelectron spectroscopies and density functional theory calculations are used to investigate the interaction between para-phenylenediamine (PPDA), an electron donor, and a polycrystalline nickel surface. The interface dipole formed upon chemisorption of one PPDA monolayer strongly modifies the work function of the nickel surface from 5.10 to 3.55 eV. The work function decrease of 1.55 eV is explained by the electron-donor character of PPDA and the modification of the electronic density at the metal surface. PPDA monolayers are composed of tilted molecules interacting via the nitrogen lone-pair and PPDA molecules chemisorbed parallel to the surface via their π-electron density. Annealing the monolayer leads to dehydrogenation of PPDA activated by the nickel surface, as found for other amines.

  • 22.
    Lindell, Linda
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Jakobsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Andersson, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Berggren, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Cornil, Jerome
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Towards Transparent Inorganic and Plastic Low-Workfunction Electrodes2005In: MRS Fall Meeting,2005, 2005Conference paper (Refereed)
  • 23.
    Lindell, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Unge, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    de Jong, Michael P
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 16, 163302-1-163302-3 p.Article in journal (Refereed)
    Abstract [en]

    In organic-based electronics, interfacial properties have a profound impact on device performance. The lineup of energy levels is usually dependent on interface dipoles, which may arise from charge transfer reactions. In many applications, metal-organic junctions are prepared under ambient conditions, where direct overlap of the organic system from the metal bands is prevented due to presence of oxides and/or hydrocarbons. We present direct experimental and theoretical evidence showing that the interface energetic for such systems is governed by exchange of an integer amount of electrons.

  • 24.
    Minkov, I.
    et al.
    Theoretical Chemistry, Royal Institute of Technology, Roslagstullsbacken 15, S-106 91 Stockholm, Sweden.
    Gel'mukhanov, F.
    Theoretical Chemistry, Royal Institute of Technology, Roslagstullsbacken 15, S-106 91 Stockholm, Sweden, Inst. of Automation and Electrometry, 630090 Novosibirsk, Russian Federation.
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Suess, C.
    Ohrwall, G.
    Öhrwall, G., Department of Physics, Uppsala University, P.O. Box 530, S-751 21 Uppsala, Sweden.
    Sorensen, S.L.
    Dept. of Synchrt. Radiation Research, Institut of Physics, Lund University, P.O. Box 118, 5-221 00 Lund, Sweden.
    Braun, Slawomir
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Murdey, R.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Agren, H.
    Ågren, H., Theoretical Chemistry, Royal Institute of Technology, Roslagstullsbacken 15, S-106 91 Stockholm, Sweden.
    Core excitations of naphthalene: Vibrational structure versus chemical shifts2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 12, 5733-5739 p.Article in journal (Refereed)
    Abstract [en]

    The initial state chemical shifts and vibrational fine structure of core excitations of naphthalene were analyzed using high-resolution x-ray photoelectron emission (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectra. The carbon atoms at peripheral sites were found to experience a small chemical shift and exhibit similar charge-vibrational coupling. The C-H stretching modes provide significant contributions to overall shape of spectra in the XPS spectra. The results show that vibrational fine structure dominates by particular C-C stretching modes, and in XPS of C2 and C3 sites also by high-energy C-H stretching modes.

  • 25.
    Osikowicz, Wojciech
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Tengstedt, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lindell, Linda
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Kugler, Thomas
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Transparent low-work-function indium tin oxide electrode obtained by molecular scale interface engineering2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, no 9, 1616-1618 p.Article in journal (Refereed)
    Abstract [en]

    Transparent low-work-function indium tin oxide (ITO) electrode was obtained by using molecular scale interface engineering. The modified ITO surface may be used as electron injecting electrode in polymer light-emitting devices. ITO surfaces, exposed to TDAE molecules, were found to be stable upon exposure to air, and to mild annealing. Photoelectron spectroscopy measurements show that the low-work-function of the modified electrode remains upon exposure to air in gentle annealing.

  • 26.
    Osikowicz, Wojciech
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Braun, Slawomir
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Tengstedt, Carl
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Energetics at Au top and bottom contacts on conjugated polymers2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 19Article in journal (Refereed)
    Abstract [en]

    Photoelectron spectroscopy was employed to examine the energetics, and therefore charge injection barriers, at top and bottom contact configurations of gold and conjugated polymers, i.e., polymer spin coated on gold and vapor-deposited gold on polymer interfaces. Very similar results are obtained for both ex situ (contaminated) and in situ (clean) prepared interfaces: a 0.7-0.8 eV decrease in the vacuum energy levels is consistently observed as compared to bare polycrystalline gold. These observations are explained by changes of the metal work function upon contacting either polymers or contaminants, associated with the reduction of the electron density tail that extends outside the metal surface. © 2006 American Institute of Physics.

  • 27.
    Osikowicz, Wojciech
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Formation of the interfacial dipole at organic-organic interfaces: C 60/polymer interfaces2007In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 19, no 23, 4213-4217 p.Article in journal (Refereed)
    Abstract [en]

    The energetics at organic-organic interfaces comprising a thin film of a p-conjugated polymer and an overlayer of fullerene C60 was investigated. Two different polymers, poly(3-hexylthiophene) or P3HT, a polymer with moderate electron donor character were investigated. P3HT films were spin-coated from 5 mg mL-1 and 20 mg mL solutions in dichlorobenzene on conductive substrates such as native oxide terminated silicon SiO x/Si and aluminum, cleaned in acetone and isopropyl alcohol prior to spin coating and UV ozone treated gold. The thickness of the resulting polymer films obtained from the solutions with high concentrations was about 20 nm and 150 nm, as determined from reflectance ellipsometry. The results suggested that integer charge transfer provides a comprehensive description of energy level alignment at interfaces of organic semiconductors.

  • 28.
    Osikowicz, Wojciech
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Sorensen, S.L.
    Lunds universitet.
    Groenendaal, L.
    AGFA-Gevaert.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Site-specific electronic structure of an oligo-ethylenedioxythiophene derivative probed by resonant photoemission2005In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 7Article in journal (Refereed)
    Abstract [en]

    A combination of conventional and resonant photoemission spectroscopy, x-ray absorption spectroscopy and ground-state quantum-chemical calculations has been used to study the valence electronic structure of a phenyl-capped 3,4-ethylenedioxythiophene oligomer, in polycrystalline thin films. The photon energy-dependent intensities of specific resonant decay channels are interpreted in terms of the spatial overlap of the excitation site and the ground-state molecular orbital involved in the decay. By making use of chemical shifts, excitations on different atomic sites are distinguished. It is demonstrated that site-specific information on the electronic structure of relatively large and complex organic systems may be obtained experimentally from non-radiative resonant decay spectra. In addition, these spectra provide relevant insight into the interpretation of near-edge x-ray absorption fine structure spectra. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

  • 29.
    Osikowicz, Wojciech
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Murdey, R.
    Giles, M.
    Merck Chemicals, University Parkway, Southampton SO16 7QD, United Kingdom.
    Heeney, M.
    Merck Chemicals, University Parkway, Southampton SO16 7QD, United Kingdom.
    Tierney, S.
    Merck Chemicals, University Parkway, Southampton SO16 7QD, United Kingdom.
    McCulloch, I.
    Merck Chemicals, University Parkway, Southampton SO16 7QD, United Kingdom.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of a novel alkylidene fluorene polymer in the pristine state2004In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 385, no 3-4, 184-188 p.Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a novel conjugated polymer, polyalkylidene fluorene has been studied using a combined experimental-theoretical approach. The densities of states in the valence band region of the new derivative, poly(9-(1'-decylundecylidene)fluorene), were measured by ultraviolet photoelectron spectroscopy and compared with electronic band-structure calculations performed in the valence effective Hamiltonian framework. The results are compared with those of similar studies on the reference polymer poly(9,9-dioctylfluorene). We report the experimentally determined ionization potential for this new material and discuss the role of substitution in altering the electronic properties of the polymer backbone. © 2003 Elsevier B.V. All rights reserved.

  • 30.
    Osikowicz, Wojciech
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Van, Der Gon A.W.D.
    Van Der Gon, A.W.D., Department of Applied Physics, Eindhoven Univ. of Technology, PO Box 513, 5600 MB Eindhoven, Netherlands.
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Groenendaal, L.
    AGFA-Gevaert N.V., R and D Mat. - Chem. Dept., Septestraat 27, B-2640 Mortsel, Belgium.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Beljonne, D.
    Serv. Chim. des Materiaux Nouveaux, CREPM, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Lazzaroni, R.
    Serv. Chim. des Materiaux Nouveaux, CREPM, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    A joint theoretical and experimental study on the electronic properties of phenyl-capped 3,4-ethylenedioxythiophene oligomers2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 19, 10415-10420 p.Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a series of phenyl-capped EDOT oligomers was studied using ultraviolet photoelectron spectroscopy, in combination with quantum-chemical methods. The bulk IP of the neutral PEDOT polymer was estimated to be 4.2 eV. The frontier band structue was predicted from the evolution of the spectral features in the studied series of oligomers.

  • 31.
    Sanchez-Carrera, R.S.
    et al.
    Sánchez-Carrera, R.S., School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400.
    Coropceanu, V.
    School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400.
    Da, Silva Filho D.A.
    Da Silva Filho, D.A., School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400.
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Murdey, R.
    Suess, C.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Bredas, J.-L.
    Brédas, J.-L., School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400.
    Vibronic coupling in the ground and excited states of oligoacene cations2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 38, 18904-18911 p.Article in journal (Refereed)
    Abstract [en]

    The vibrational coupling in the ground and excited states of positively charged naphthalene, anthracene, tetracene, and pentacene molecules is studied on the basis of a joint experimental and theoretical study of ionization spectra using high-resolution gas-phase photoelectron spectroscopy and first-principles correlated quantum-mechanical calculations. Our theoretical and experimental results reveal that, while the main contribution to relaxation energy in the ground state of oligoacene systems comes from high-energy vibrations, the excited-state relaxation energies show a significant redistribution toward lower-frequency vibrations. A direct correlation is found between the nature of the vibronic interaction and the pattern of the electronic state structure. © 2006 American Chemical Society.

  • 32.
    Tengstedt, Carl
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Parker, I.D.
    Dupont Displays, Santa Barbara, California.
    Hsu, C-H.
    Dupont Displays, E.I. DuPont de Nemours and Company, Wilmington, Delaware.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Fermi-level pinning at conjugated polymer interfaces2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 5, 53502- p.Article in journal (Refereed)
    Abstract [en]

    Photoelectron spectroscopy has been used to map out energy level alignment of conjugated polymers at various organic-organic and hybrid interfaces. Specifically, we have investigated the hole-injection interface between the substrate and light-emitting polymer. Two different alignment regimes have been observed: (i) Vacuum-level alignment, which corresponds to the lack of vacuum-level offsets (Schottky–Mott limit) and (ii) Fermi-level pinning, where the substrate Fermi level and the positive polaronic level of the polymer align. The observation is rationalized in terms of spontaneous charge transfer whenever the substrate Fermi level exceeds the positive polaron/bipolaron formation energy per particle. The charge transfer leads to the formation of an interfacial dipole, as large as 2.1 eV.

  • 33.
    Tsao, H.N.
    et al.
    Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
    Pisula, W.
    Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany, Evonik Degussa GmbH, Process Technology and Engineering, Process Technology New Processes, Rodenbacher Chaussee 4, 63457 Hanau, Germany.
    Liu, Z.
    Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Mullen, K.
    Müllen, K., Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
    From ambi- To unipolar behavior in discotic dye field-effect transistors2008In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 20, no 14, 2715-2719 p.Article in journal (Refereed)
    Abstract [en]

    A study was conducted to demonstrate solution-processable ambipolar organic field-effect transistors based on a discotic dye. Such single component devices allow the study of the influence of supramolecular ordering on FET charge transport properties. These transistors exhibited ambipolarity even without any structural order. The absence of p-type behavior could not be explained by the increase of hole injection barrier or by interface trapping. It was rather observed that the change in morphology most probably lead to such a phenomenon. These findings further suggest that besides charge injection barriers and interface trapping, structural composition, that is, microscopic domain boundaries together with local defects in one-dimensional columnar systems, also trigger the loss of ambipolarity owing to lowering of the minority charge carrier mobility.

  • 34.
    Zotti, G.
    et al.
    Istituto CNR l'Energetica Interfasi, C.o Stati Uniti 4, 35127 Padova, Italy.
    Zecchin, S.
    Istituto CNR l'Energetica Interfasi, C.o Stati Uniti 4, 35127 Padova, Italy.
    Schiavon, G.
    Istituto CNR l'Energetica Interfasi, C.o Stati Uniti 4, 35127 Padova, Italy.
    Louwet, F.
    R and D Materials Research, Chemistry Department, Agfa Gevaert N.V., Septelaan 27, B-2640 Mortsel, Belgium.
    Groenendaal, L.
    R and D Materials Research, Chemistry Department, Agfa Gevaert N.V., Septelaan 27, B-2640 Mortsel, Belgium.
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electrochemical and XPS studies toward the role of monomeric and polymeric sulfonate counterions in the synthesis, composition, and properties of poly(3,4-ethylenedioxythiophene)2003In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 36, no 9, 3337-3344 p.Article in journal (Refereed)
    Abstract [en]

    Electrochemically prepared poly(3,4-ethylenedioxythiophene) (PEDT) poly(styrenesulfonate) (PSS), produced from acidic (PSSH) and basic (PSSNa) PSS, was characterized by cyclic voltammetry CV, UV-vis spectroscopy, in situ conductivity, and XPS spectroscopy and was compared with electrochemically prepared PEDT/tosylate and chemically prepared PEDT/PSS. CV analysis shows that the polymer synthesis is strongly affected by the nucleophilic character of the counteranion. Although CV and UV-vis spectroscopy show that the structure and degree of polymerization (oligomeric, ca. 10 EDT units) of the PEDT backbone is the same for all polymers, XPS is able to explain the different conductivity values for these materials (ranging from 1 S cm-1 for PEDT/PSSNa to 400-450 S cm-1 for PEDT/tosylate) based on doping level and composition. In particular, critical results are observed to be the ratios between sulfonate and thiophene units in the polymers: the higher the PEDT concentration, the higher the conductivity. XPS also explains by solvent-induced nanometer-scale segregation between PEDT/PSS and excess PSS particles the often reported conductivity enhancement of chemically prepared PEDT/PSS upon treatment with polar solvents.

1 - 34 of 34
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