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  • 1.
    Bantikassegn, W.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, Faculty of Science & Engineering.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Absence of Schottky barrier formation in junctions of Al and polypyrrole-polyelectrolyte polymer complexes1993In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 224, no 2, 232-236 p.Article in journal (Refereed)
    Abstract [en]

    Thin films of conducting polypyrrole doped with large polymeric anions of polystyrene-sulphonate are electrochemically prepared to study the metal/polymer junctions. Aluminium and gold contacts are vacuum deposited to form metal/polymer/gold sandwich structures for current-voltage characterization. Photoelectron spectroscopy, using UV and X-ray photons, is carried out to investigate the possible causes of current limitation in the Al/PPy(PSS) junction.

  • 2.
    Bantikassegn, W.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Proceedings of the International Conference on Science and Technology of Synthetic Metals Electronic properties of polypyrrole (polystyrene-sulphonate)/metal junctions1993In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 55, no 1, 36-42 p.Article in journal (Refereed)
    Abstract [en]

    The nature of polymer/metal interfaces is decisive for the operation of polymer based electronic devices. At such interfaces charge transport may be affected by barrier formation, or by formation of insulating interfaces of various types. We have prepared thin films of conducting polypyrrole doped with large polymeric anions of polystyrenesulphonate for studies in metal/polymer junctions. Aluminium and gold contacts are vacuum deposited to form metal/polymer/gold sandwich structures. The current-voltage characteristics show that the interface between polypyrrole and gold is ohmic with no current limitation. However, the aluminium/polypyrrole interface forms highly resistive and nonohmic contacts. Photoelectron spectroscopy using UV and X-ray photons reveals a decrease of the work function upon Al deposition, reactions between Al and the sulphonate anions, and immediate oxidation of the aluminium upon exposure to oxygen. These observations corroborate the interpretation that the current limitation found at Al/polypyrrole junctions is due to formation of insulating aluminium oxide, not excluding reactions between the metal and dopant. It is also pointed out that interfaces between reactive metals and polymers are prone to such oxide interface formation, considering the high diffusivity of oxygen in many polymers.

  • 3. Birgerson, J.
    et al.
    Janssen, F.J.J.
    Department of Applied Physics, Dutch Polymer Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands.
    Denier, van der Gon A.W.
    Tsukahara, Y.
    Dept. of Chem. and Mat. Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
    Kaeriyama, K.
    Dept. of Chem. and Mat. Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Doped polymeric cathodes for PPV/Al based LEDs2002In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 132, no 1, 57-61 p.Article in journal (Refereed)
    Abstract [en]

    The effect of Li-doping in poly(para-phenylenevinylene) (PPV) based light emitting devices has been studied. In a standard structure with an indium tin oxide (ITO) anode, poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT-PSS)-layer and an active PPV-layer, the effects of a thin (around 1 Å) Li-layer and a thin layer, (50 Å), of a large bandgap polymer, poly(2,5-diheptyl-1,4-phenylene-alt-1,4-naphthylene) (P14NHP) between the PPV and the aluminum cathode have been studied in terms of IV-characteristics and efficiency. The Li-atoms dope the interfacial layer of the PPV as seen by photoelectron spectroscopy. A thin layer of Li improves the charge balance by decreasing the energy barrier for injection of electrons for the Al/Li/PPV/PEDOT-PSS/ITO device. The efficient electron injection originates from a Fermi level alignment between the doped polymer and the aluminum cathode, which reduces the energy barrier. A thin layer of the large bandgap polymer P14NHP, between the PPV and Al contact, increases the light output and efficiency by blocking the holes. In addition, it may also reduce the light quenching by moving the region of recombination away from the Al-contact. The addition of a Li-layer on top of P14NHP leads to an increase of the quantum efficiency, because of better electron injection. © 2002 Elsevier Science B.V. All rights reserved.

  • 4. Birgerson, J.
    et al.
    Johansson, N.
    Pohl, A.
    Logdlund, M.
    Lögdlund, M., ACREO AB, Bredgatan 34, S-602 21 Norrköping, Sweden.
    Tsukahara, Y.
    Dept. of Chem. and Mat. Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
    Kaeriyama, K.
    Dept. of Chem. and Mat. Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of some conjugated polymers for electron transport2001In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 122, no 1, 67-72 p.Article in journal (Refereed)
    Abstract [en]

    The chemical and electronic structure of three different, strictly alternating copolymers, poly(2,5-diheptyl-1,4-phenylene-alt-1,4-naphthylene) (P14NHP), poly(2,5-diheptyl-1,4-phenylene-alt-2,6-naphthylene) (P26NHP) and poly(2,5-diheptyl-1,4-phenylene-alt-9,10-anthrylene) (P910AHP), have been studied by photoelectron spectroscopy and optical absorption spectroscopy. The experimental results have been analyzed using the results of quantum chemical calculations. In the geometrical structure of all three of the polymers there are large torsion angles between the phenylene unit and the naphthylene or anthrylene units. These large torsion angles lead to localization of the p-electron wave functions, and minimal conjugation along the polymer backbone. For all three polymers, the highest occupied molecular orbital is completely localized to the naphthylene or anthrylene unit. The frontier molecular orbital wave functions are very reminiscent of the highest occupied orbitals of the isolated naphthalene or anthracene molecules. The optical absorption spectra of all three polymers verify the existence of large optical band gaps, consistent with the large torsion angels. The first several optical transitions in the polymers are also very reminiscent of the transitions in single naphthalene and anthracene molecules.

  • 5. Birgerson, J.
    et al.
    Keil, M.
    Luo, Y.
    Theoretical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Svensson, S.
    Department of Physics, Uppsala University, S-751 21 Uppsala, Sweden.
    Agren, H.
    Ågren, H., Theoretical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    A study of the electronic structure of ethylenedioxythiophene in gas phase using NEXAFS and quantum chemical calculations2004In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 392, no 1-3, 100-104 p.Article in journal (Refereed)
    Abstract [en]

    Near-edge X-ray absorption fine structure spectroscopy spectra of ethylenedioxythiophene has been recorded in gas phase at the carbon K-edge, sulphur L-edge and oxygen, K-edge. The experimental data has been interpreted with the help of a modified density functional code deMon. The good agreement between the calculated spectra and the measured one allows us to assign all observed resonances. The existence of p* resonances in both the measured and the calculated OK-edge adsorption spectrum demonstrate that the delocalized p-system of the thiophene part of the molecule is extended up to the oxygen atoms of the molecule. © 2004 Elsevier B.V. All rights reserved.

  • 6.
    Braun, Slawomir
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    de Jong, Michel P.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . 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.
    Energy level alignment of organic interfaces under reversal of deposition sequence: the role of Fermi level pinning2007Article in journal (Refereed)
  • 7.
    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.

  • 8.
    Braun, Slawomir
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. 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.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Fermi level equilibrium at donor-acceptor interfaces in multi-layered thin film stack of TTF and TCNQ2010In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 11, no 2, 212-217 p.Article in journal (Refereed)
    Abstract [en]

    Organic hetero-junctions in multi-layered thin film stacks comprising alternate layers of the molecular donor-tetrathiafulvalene (TTF) and the acceptor - tetracyanoquinodimethane (TCNQ), have been studied by ultraviolet photoelectron spectroscopy ( UPS). We show that the energy level alignment at the organic-organic interfaces in the stacks depends only upon the relative energy structure of the donor and acceptor molecules, in particular, the molecular integer charge transfer (ICT) states. The observed interfacial dipoles, across the multi-layered organic stacks, correspond to the difference in energy between the positive and the negative charge transfer states of the molecules constituting the interface. Consequently, Fermi level across the multi-layer system is pinned to those states, since the energetic conditions for the charge transfer across the interface are fulfilled. Hence the energy level alignment at donor - acceptor interfaces studied can be rationalized on the basis of integer charge transfer model (ICT-model). Moreover, we present the photoelectron spectra where 0.85 eV shift of the highest occupied molecular orbital (HOMO) of TTF during formation of TCNQ over-layer is directly observed. These studies contribute to the understanding of the nature of the offset between the frontier electronic levels of the donor and acceptor components which is of high importance in the engineering of efficient organic solar cells.

  • 9.
    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.

  • 10.
    Braun, Slawomir
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . 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.
    Fermi level pinning at interfaces with tetrafluorotetracyanoquinodimethane (F4-TCNQ): The role of integer charge transfer states2007In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 438, no 4-6, 259-262 p.Article in journal (Refereed)
    Abstract [en]

    The energy level alignment of vacuum deposited molecular films of tetrafluorotetracyanoquinodimethane (F4-TCNQ) on various substrates has been studied by photoelectron spectroscopy. The interfaces studied span the work function range from 3.45 to 5.8 eV. In this range, the Fermi level of the substrate is pinned in proximity to LUMO level. This indicates that a charge transfer mechanism is responsible for the observed alignment scheme. The photoelectron emission study of sub-monolayer of F4-TCNQ revealed presence of electrons in the charge transfer states at the interface. In this context the electronic structure of neutral and negatively charged F4-TCNQ has been studied theoretically and by photoelectron spectroscopy.

  • 11.
    Braun, Slawomir
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . 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.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Energy-Level Alignment at Organic/Metal and Organic/Organic Interfaces2009In: ADVANCED MATERIALS, ISSN 0935-9648, Vol. 21, no 14-15, 1450-1472 p.Article, review/survey (Refereed)
    Abstract [en]

    In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).

  • 12. Bredas, JL
    et al.
    Marder, SR
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa - Tribute2002In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 35, no 4, 1137-1139 p.Other (Other academic)
  • 13.
    Bröms, P.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Xing, K. Z.
    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.
    Dannetun, Per
    Groupe de Physique des Solides, Tour 23-2, place Jussieu, F-752 51 Paris Cedex 05, France.
    Cornil, J.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Santos, D.A. dos
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Moratti, S. C.
    University Chemical Laboratory, University of Cambridge, Cambridge CB2 1EW, UK.
    Holmes, A. B.
    University Chemical Laboratory, University of Cambridge, Cambridge CB2 1EW, UK.
    Friend, R. H.
    Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
    Optical absorption studies of sodium doped poly(cyanoterephthalylidene)1994In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 67, no 1-3, 93-96 p.Article in journal (Refereed)
    Abstract [en]

    The effects of doping poly(cyanoterephthalylidene) with sodium in ultrahighvacuum been studied by optical absorption spectroscopy. Upon doping, new optical transitions are observed within the bandgap; the characteristics of these transitions are consistent with the formation of bipolarons. The optical absorption results are confirmed by direct measurements of the doping-induced gap states using ultraviolet photoelectron spectroscopy.

  • 14.
    Cacialli, F.
    et al.
    Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
    Feast, W.James
    IRC in Polymer Science and Technology, Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
    Friend, R.H.
    Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, United Kingdom.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Lovenich, P.W.
    Lövenich, P.W., IRC in Polymer Science and Technology, Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Synthesis and characterisation of poly(distyrylbenzene-block-hexa(ethylene oxide)) and its fluorinated analogue - Two new block copolymers and their application in electroluminescent devices2002In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 43, no 12, 3555-3561 p.Article in journal (Refereed)
    Abstract [en]

    Two new soluble block copolymers are reported in which chromophores and hexa(ethylene oxide) units alternate along the polymer backbone. In polymer 1 the chromophore was the distyrylbenzene unit. The polymer was synthesised via the Wittig reaction and the ionization potential of 5.4 ± 0.2 eV was measured by cyclic voltammetry and photoelectron spectroscopy. Polymer 1 showed a high solid-state photoluminescence efficiency (34%) and was used to make efficient (0.5 cd/A) light emitting diodes (LEDs). Polymer 1 was also used in light emitting cells, these showed luminescence in reverse bias and a reduced turn-on voltage compared to the LEDs. Polymer 2, in which the chromophore was dodecafluoro-distryrylbenzene, was prepared via the Horner-Wittig reaction and showed an ionization potential of 6.25 ± 0.15 eV and a solid-state photoluminescence efficiency of 17%. It was used as electron-conducting layer in a LED but failed to give significant electroluminescence. The optical energy gap for both polymers was 3.0 eV. © 2002 Published by Elsevier Science Ltd.

  • 15.
    Crispin, Annica
    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.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    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.
    Transition between energy level alignment regimes at a low band gap polymer-electrode interfaces2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, no 21Article in journal (Refereed)
    Abstract [en]

    The energy level alignment at interfaces between a low band gap conjugated polymer and various electrodes is investigated using ultraviolet photoemission spectroscopy. When the electrode work function is lower (higher) than the negative (positive) polaronic level of the polymer, the Fermi level is pinned to the negative (positive) polaronic level. These Fermi level pinning regimes suggest a spontaneous electron transfer from or towards the electrode resulting in an interfacial dipole of different orientation. On the contrary, when the substrate work function is intermediate, there is no charge transfer and the energy level alignment across the interface follows the Schottky-Mott limit. © 2006 American Institute of Physics.

  • 16.
    Crispin, Annica
    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.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Dos, Santos D.A.
    Dos Santos, D.A., Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Cornil, J.
    Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Johansson, N.
    Bauer, J.
    Covion Organic Semiconductors GmbH, Industrial Park Hoechst, D-65926 Frankfurt, Germany.
    Weissortel, F.
    Weissörtel, F., Electrochemistry and Optoelectronic Materials, FB 6, University Duisburg, D-47048 Duisburg, Germany.
    Salbeck, J.
    Electrochemistry and Optoelectronic Materials, FB 6, University Duisburg, D-47048 Duisburg, Germany, Macromolecular Chemistry and Molecular Materials, FB 18, University Kassel, D-34132 Kassel, Germany.
    Bredas, J.L.
    Brédas, J.L., Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium, Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, United States.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Influence of dopant on the electronic structure of spiro-oligophenyl-based disordered organic semiconductors2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 116, no 18, 8159-8167 p.Article in journal (Refereed)
    Abstract [en]

    The influence of the dopant on the electronic structure of spiro-oligophenyl-based disordered organic semiconductors was studied by means of photoelectron spectroscopy. With lithium atoms as dopants, two charges were stored on the same spiro branch in the form of bipolarons, for spiro-quarterphenyl and spiro-sexiphenyl. For doping with the sodium atoms, the size of the counter ions made it less energetically desirable to store two charges onto a single branch, and the charged species were polarons independent of the level of doping which was confirmed by optical absorption data.

  • 17.
    Crispin, Annica
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Jonsson, A.
    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 .
    Aluminum-barium interfaces on some processable poly(p-phenylene vinylene) polymers studied by photoelectron spectroscopy2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 115, no 11, 5252-5257 p.Article in journal (Refereed)
    Abstract [en]

    The control of the deposition of metals on the surface of conjugated polymers determined the electronic properties of the electrical contacts. X ray photoelectron spectroscopy (XPS) and ultraviolet photon spectroscopy (UPS) was used to study the influence of an intermediate layer of barium atoms on the chemical effects that occured during the deposition of aluminium atoms of substituted poly(p-phenylvinylene) polymers. The thin films were prepared on gold substrates for spectroscopy by spin coating techniques. The diffusion of the aluminium atoms occured when the side grops were bulky and therby resulted in porous polymer films.

  • 18.
    Crispin, Xavier
    et al.
    University of Mons, Belgium.
    Bureau, C.
    CEA Saclay, France;.
    Geskin, V. M.
    University of Mons, Belgium.
    Lazzaroni, R.
    University of Mons, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Bredas, J. L.
    University of Mons, Belgium.
    Chemisorption of acrylonitrile on the Cu(100) surface: A local density functional study1999In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 111, no 7, 3237-3251 p.Article in journal (Refereed)
    Abstract [en]

    The possibility of chemically grafting polyacrylonitrile onto transition metal electrodes via electropolymerization leads to promising applications in the fields of corrosion protection or metal surface functionalization. The initial step of the electrografting mechanism is the adsorption of the acrylonitrile monomer on the metal surface from solution. Here, we investigate theoretically this adsorption process on the copper (100) surface; Density Functional Theory is used in the Local Spin Density approximation to describe the electronic and structural properties of acrylonitrile adsorbed on copper clusters. The chemisorption of acrylonitrile on the copper surface is confirmed experimentally via X-Ray Photoelectron Spectroscopy. The thermodynamic characteristics of the adsorption process are also studied via statistical mechanics. Finally, determining the influence of the copper cluster size on the adsorption of acrylonitrile allows to extrapolate the properties of the acrylonitrile/Cu(100) surface from those of acrylonitrile/copper clusters. (C) 1999 American Institute of Physics. [S0021-9606(99)70231-X].

  • 19.
    Crispin, Xavier
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Cornil, J.
    Université de Mons-Hainaut.
    Friedlein, Rainer
    Linköping University, Department of Physics, Chemistry and Biology.
    Okudaira, K. K.
    Chiba University.
    Lemaur, V
    Université de Mons-Hainaut.
    Crispin, Annica
    Linköping University, Department of Physics, Chemistry and Biology.
    Kestemont, G.
    Université Libre de Bruxelles.
    Lehmann, M.
    Université Libre de Bruxelles.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lazzaroni, R.
    Université de Mons-Hainaut.
    Geerts, Y
    Université Libre de Bruxelles.
    Wendin, G.
    Chalmers University of Technology.
    Ueno, N.
    Chiba University.
    Brédas, J.-L.
    Université de Mons-Hainaut.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology.
    Electronic delocalization in discotic liquid crystals: A joint experimental and theoretical study2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 38, 11889-11899 p.Article in journal (Refereed)
    Abstract [en]

    Discotic liquid crystals emerge as very attractive materials for organic-based (opto)electronics as they allow efficient charge and energy transport along self-organized molecular columns. Here, angle-resolved photoelectron spectroscopy (ARUPS) is used to investigate the electronic structure and supramolecular organization of the discotic molecule, hexakis(hexylthio)diquinoxalino[2,3-a:2′,3′-c]phenazine, deposited on graphite. The ARUPS data reveal significant changes in the electronic properties when going from disordered to columnar phases, the main feature being a decrease in ionization potential by 1.8 eV following the appearance of new electronic states at low binding energy. This evolution is rationalized by quantum-chemical calculations performed on model stacks containing from two to six molecules, which illustrate the formation of a quasi-band structure with Bloch-like orbitals delocalized over several molecules in the column. The ARUPS data also point to an energy dispersion of the upper π-bands in the columns by some 1.1 eV, therefore highlighting the strongly delocalized nature of the π-electrons along the discotic stacks.

  • 20.
    Crispin, Xavier
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Geskin, V.
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Cornil, J.
    Lazzaroni, R.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Bredas, J.-L.
    Characterization of the interface dipole at organic/metal interfaces2002In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, no 27, 8131-8141 p.Article in journal (Refereed)
    Abstract [en]

    In organics-based (opto)electronic devices, the interface dipoles formed at the organic/metal interfaces play a key role in determining the barrier for charge (hole or electron) injection between the metal electrodes and the active organic layers. The origin of this dipole is rationalized here from the results of a joint experimental and theoretical study based on the interaction between acrylonitrile, a p-conjugated molecule, and transition metal surfaces (Cu, Ni, and Fe). The adsorption of acrylonitrile on these surfaces is investigated experimentally by photoelectron spectroscopies, while quantum mechanical methods based on density functional theory are used to study the systems theoretically. It appears that the interface dipole formed at an organic/metal interface can be divided into two contributions: (i) the first corresponds to the "chemical" dipole induced by a partial charge transfer between the organic layers and the metal upon chemisorption of the organic molecules on the metal surface, and (ii) the second relates to the change in metal surface dipole because of the modification of the metal electron density tail that is induced by the presence of the adsorbed organic molecules. Our analysis shows that the charge injection barrier in devices can be tuned by modulating various parameters: the chemical potential of the bare metal (given by its work function), the metal surface dipole, and the ionization potential and electron affinity of the organic layer.

  • 21.
    Crispin, Xavier
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Jakobsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Grim, P.C.M.
    KUL, Belgien.
    Andersson, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Volodin, A.
    KUL, Belgien.
    van Haesendonch, C.
    KUL, Belgien.
    van der Auweraer, M.
    KUL, Belgien.
    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.
    The origin of the high conductivity of poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) (PEDOT-PSS) plastic electrodes2006In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 18, no 18, 4354-4360 p.Article in journal (Refereed)
    Abstract [en]

    The development of printed and flexible (opto)electronics requires specific materials for the device's electrodes. Those materials must satisfy a combination of properties. They must be electrically conducting, transparent, printable, and flexible. The conducting polymer poly(3,4-ethylenedioxythiophene) - poly-(styrenesulfonate) (PEDOT-PSS) is known as a promising candidate. Its conductivity can be increased by 3 orders of magnitude by the secondary dopant diethylene glycol (DEG). This "secondary doping" phenomenon is clarified in a combined photoelectron spectroscopy and scanning probe microscopy investigation. PEDOT-PSS appears to form a three-dimensional conducting network explaining the improvement of its electrical property upon addition of DEG. Polymer light emitting diodes are successfully fabricated using the transparent plastic PEDOT-PSS electrodes instead of the traditionally used indium tin oxide. © 2006 American Chemical Society.

  • 22.
    Crispin, Xavier
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Geskin, V.M.
    Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium, Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, United States.
    Bredas, J.L.
    Brédas, J.L., Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, 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 .
    Understanding the initial stages of polymer grafting on metals: A photoelectron spectroscopy study of acrylonitrile adsorption on transition metal surfaces2001In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 121, no 1-3, 57-74 p.Article in journal (Refereed)
    Abstract [en]

    X-ray and UV photoelectron spectroscopies show that acrylonitrile is chemisorbed on iron, nickel and copper polycrystalline surfaces via the carbon and nitrogen atoms. Depending on the conditions used, different adsorption geometries are found. The molecules can either be adsorbed flat on the surface and chemically bound by a (2pp)-(3d/4s) overlap via both the C=C double bond and the C=N nitrile group or they can be adsorbed perpendicular to the surface via a covalent interaction between the nitrogen lone pair and the 3d-4s levels of the metals. Analysis of the XPS data obtained on molecular mono-layers chemisorbed on metal surfaces emphasizes the importance of initial-state effects (charge transfer upon chemisorption, contribution of the metal surface dipole) and final-state effects (metal screening and polarization effect within the mono-layer). The correlation between the XPS and UPS data illustrates the importance of the metal surface dipole in understanding the workfunction changes upon molecular adsorption on metal surfaces. © 2001 Elsevier Science B.V. All rights reserved.

  • 23.
    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.

  • 24. 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.

  • 25.
    Dannetun, P.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lazzaroni, R.
    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, Faculty of Science & Engineering.
    Scherr, E.
    Department of Chemistry, University of Pennsylvania Philadelphia, USA.
    Sun, Y.
    Department of Chemistry, University of Pennsylvania Philadelphia, USA.
    MacDiarmid, A. G.
    Department of Chemistry, University of Pennsylvania Philadelphia, USA.
    The eletronic structure of emeraldine doped in situ from HCl in the gas phase as studied by photoelectron spectroscopy1991In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 41, no 1-2, 645-648 p.Article in journal (Refereed)
    Abstract [en]

    The chemical and electronic structure of spin-coated films of polyaniline in the emeraldine state, treated in-situ with HCl in the gas phase, have been studied for the first time by means of X-ray Photoelectron Spectroscopy (XPS) and Ultra-violet Photoelectron Spectroscopy (UPS). Ultra thin films, of about several hundreds of Ångströms thickness, were spin-coated from a solution of chemically prepared emeraldine in NMP, onto substrates of aluminum or silicon. The salt forms were prepared both by (a) “wet” doping in 1M HCl and (b) the in-situ treatment of the films with HCl in the gas phase. With XPS three different types of chlorine have been observed, two ionic and one covalent. With UPS the valence band spectra of the doped and undoped state, are studied.

  • 26.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Boman, Magnus
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons‐Hainaut, Belgium.
    Fredriksson, C.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons‐Hainaut, Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons‐Hainaut, Belgium.
    Zamboni, R.
    Istituto di Spettroscopia Molecolare, CNR, Bologna, Italy.
    Taliani, C.
    Istituto di Spettroscopia Molecolare, CNR, Bologna, Italy.
    The chemical and electronic structure of the interface between aluminum and polythiophene semiconductors1993In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 99, no 1, 664-672 p.Article in journal (Refereed)
    Abstract [en]

    We have investigated the chemical nature and the electronic structure of the interface between a low work function metal,aluminum, and a conjugated polymersemiconductor, polythiophene. We have studied the initial stages of the interface formation by depositing the metal onto the surface of a polymer film. Charge transfer processes between the metal and the polymer are analyzed using core‐level x‐ray photoelectron spectroscopy (XPS); the evolution upon metallization of the valence electronic levels directly related to the polymerelectronic structure is followed with ultraviolet photoelectron spectroscopy (UPS). With these techniques, we investigate the deposition of aluminum on two polythiophene systems (i) the alkyl‐substituted poly‐3‐octylthiophene and (ii) the α‐sexithiophene oligomer. The experimental data are compared to the results of a recent quantum chemical study on model systems consisting of thiophene oligomers (up to sexithiophene) interacting with a few Al atoms. The interaction of polythiophene with Al atoms is found to modify dramatically the structure of the conjugated backbone, as strong carbon–aluminum bonds are formed in the α positions of the thiophene rings. A large charge transfer takes place from the Al atoms to the polymer chain, and the upper π levels of the polymer are strongly affected. The metallization is contrasted to the doping of conjugated polymers with alkali metals

  • 27.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fauquet, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kaerijama, K.
    National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305, Japan.
    Sonoda, Y.
    National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305, Japan.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Interface formation between poly(2,5-diheptyl-p-phenylenevinylene) and calcium: implications for light-emitting diodes1994In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 67, no 1-3, 133-136 p.Article in journal (Refereed)
    Abstract [en]

    The early stages of metal/polymer interface formation between calcium and poly(2,5-diheptyl-p-phenylenevinylene) (PDHPV) have been studied using both X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Charge transfer is observed from the metal atoms to the polymer; as a result the calcium atoms at the interface are ionic, and negative bipolarons appear as the charge-carrying species on the polymer chains. This n-type doping of PDHPV by calcium leads to the appearance of new electronic states in the polymer bandgap. The calcium atoms appear to diffuse into the near surface region of the polymer, rather than forming a well-defined overlayer on the organic films.

  • 28.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lögdlund, Michael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Boman, Magnus
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Mons Belgium.
    Fredriksson, C.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Mons Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Mons Belgium.
    Graham, S.
    Cavendish Laboratory, University of Cambridge, Cambridge, UK.
    Friend, R. H.
    Cavendish Laboratory, University of Cambridge, Cambridge, UK.
    Holmes, A. B.
    University Chemical Laboratory, Lensfield road, Cambridge, UK.
    Zamboni, R.
    Instituto di Spettroscopia Molecolare, Bologna, Italy.
    Taliani, C.
    Instituto di Spettroscopia Molecolare, Bologna, Italy.
    Proceedings of the International Conference on Science and Technology of Synthetic Metals The chemical and electronic structure of the interface between aluminum and conjugated polymers or molecules1993In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 55, no 1, 212-217 p.Article in journal (Refereed)
    Abstract [en]

    The interaction between aluminum and α-ω-diphenyltetradecaheptaenee (DP7), α-sexithienyl (6T), and poly(p-phenylenevinylene) (PPV), respectively have been studied using both X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS). The UPS valence band spectra, are interpreted with the help of quantum chemical calculations based upon Modified Neglect of Diatomic Overlap (MNDO), Valence Effective Hamitonian (VEH) and ab initio Hartree-Fock methods. DP7 is a model molecule for polyacetylene, while 6T is a model molecule (an oligomer) of polythiophene. The results indicate that aluminum reacts strongly with the surfaces of all of the materials studied. The π-electronic structure of each material was strongly modified. Furthermore, aluminum reacts preferentially with the polyene partof DP7, with the vinylene part of PPV, and with the α-carbons of the thiophene nits of 6T.

  • 29.
    Dannetun, Per
    et al.
    Groupe de Physique des Solides, Tour 23-2, place Jussieu, 752 51 Paris Cedex 05, France.
    Lögdlund, Michael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fauquet, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Beljonne, D.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, place du Parc 20, B-7000 Mons, Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, place du Parc 20, B-7000 Mons, Belgium.
    Bässler, H.
    Fachbereich Physikalische Chemie und Zentrum für Materialwissenschaften der Phillips-Universität, Hans-Meerwein-Strasse, W-3550 Marburg, Germany.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    The evolution of charge-induced gap states in degenerate and non-degenerate conjugated molecules and polymers as studied by photoelectron spectroscopy1994In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 67, no 1, 81-86 p.Article in journal (Refereed)
    Abstract [en]

    We report the results of ultraviolet photoelectron spectroscopy (UPS) studies of the interaction between sodium and conjugated systems for a series of diphenylpolyees and diffrent oligomers of poly(p-phenylenevinylene) (PPV). The diphenylpolyenes include molecules containing two (i.e., stilbene) to 14 carbon atoms in the polyene part; stilbene itself can also be considered as a phenyl-capped monomer of PPV. Furthermore, a PPV oligomer with three phenylene units, as well as PPV itself, has been studied. The experimental results are interpreted with the help of quantum-chemical calculations using the Hartree-Fock semi-empirical Austin Model 1 (AM1) and valence-effective Hamiltonian (VEH) methods. An important result is that all the systems react strongly with sodium; at high doping levels two new doping-induced states are detected above the valence band edge of the pristine material. In the case of saturation-doped diphenylpolyenes (i.e., two sodiums per molecule), the new states can be discussed in terms of soliton-antisoliton pairs confined within the polyene part of the molecules; in contrast, the self-localized states induced in PPV and its oligomers have to be referred to as bipolarons.

  • 30.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lögdlund, Michael
    Service de Chimie des Matériaux Nouveaux, Université de Mons‐Hainaut, Place du Parc 20, B‐7000 Mons, Belgium.
    Fredriksson, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons‐Hainaut, Place du Parc 20, B‐7000 Mons, Belgium.
    Fauquet, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Spangler, C. W.
    Department of Chemistry, Northern Illinois University, Dekalb, Illinois 60115, USA.
    Bredás, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons‐Hainaut, Place du Parc 20, B‐7000 Mons, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Reactions of low work function metals Na, Al, and Ca on α,ω-€diphenyltetradecaheptaene. Implications for metal/polymer interfaces1994In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 100, no 9, 6765-6771 p.Article in journal (Refereed)
    Abstract [en]

    The interactions between different low work function metals aluminium,calcium and sodium, and α,ω‐diphenyltetradecaheptaene, a model molecule for certain conjugated polymers, have been investigated using both x‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The spectra are interpreted with the help of the results of quantum chemical calculations performed within the local spin density (LSD) approximation methodology. The metals are found to interact with the conjugated system in very different ways. Aluminium forms a covalent bond, which strongly modifies the π‐electronic structure of the conjugated molecule, while both the sodium and the calcium atoms act as doping agents, inducing new states in the otherwise forbidden bandgap. These new gap states can be viewed as a soliton–antisoliton pair for the Na/DP7 and a bipolaronic‐like defect for Ca/DP7.

  • 31.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lögdlund, Michael
    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.
    Fredriksson, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Holmes, A. B.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Brown, A.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Graham, S.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Friend, R. H.
    Cavendish Laboratory , University of Cambridge Cambridge , CB3 OHE, England.
    Lhost, O.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    New Results on Metal-Polymer Interfaces1993In: Molecular Crystals and Liquid Crystals, ISSN 1542-1406, E-ISSN 1563-5287, Vol. 228, no 1, 43-48 p.Article in journal (Refereed)
    Abstract [en]

    New results on studies of the early stages of formation of the aluminum-poly(p-phenylenevinylene) interface are presented.

  • 32.
    Dannetun, Per
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lögdlund, Michael
    Université de Mons-Hainaut, Belgium.
    Spangler, C. W.
    Northen Illinois University, USA.
    Bredas, J. L.
    Université de Mons-Hainaut, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. william.r.salaneck@liu.se.
    Evolution of Charge-Induced Gap States in Short Diphenylpolyenes as Studied by Photoelectron Spectroscopy1994In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, The Journal of Physical Chemistry, Vol. 98, no 11, 2853-2858 p.Article in journal (Refereed)
    Abstract [en]

    The evolution of doping-induced electronic states within the otherwise forbidden energy gap has been studied as a function of the polyene length in a series of diphenylpolyenes. The chemical and electronic structures ha ve been studied using both X-ray and ultraviolet photoelectron spectroscopies. The results are interpreted with the help of quantum chemical calculations, performed using the semiempirical Austin Model 1 and valence effective Hamiltonian methods. The molecules studied area series of diphenylpolyenes, DPx, with x = 1-7 C=C double bonds in the pol yene part of the molecule. Since the frontier or bitals of the diphenylpolyenes are localized on the polyene chain portion of the molecule, there is a high degree of separation of the phenyl and polyene parts of the 11"-systems. Hence, many chemical and electronic properties of diphenylpolyenes are expected to be similar to those of short-chain trans-polyacetylene. For the longer molecules, n = 6 or 7, the present results indicate the presence of doubly charged, interacting soliton-antisoliton pairs, which appear as two new energy levels in the otherwise forbidden energy gap. In diphenyldecaheptaene to stilbene, i.e. 1 ≤ x ≤ 5, however, a singly charged state is formed at intermediate doping levels, after which the soliton-antisoliton pairs appear for the fully doubly charged systems. These results show that, remarkably, even for very short polyene  segments, charges transferred are stored in the form of ( confined) solitons.

  • 33. 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.

  • 34.
    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.

  • 35.
    de Jong, Michel P
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Dediu, V.A.
    ISMN-Bo CNR, via Gobetti 101, 40129 Bologna, Italy.
    Taliani, C.
    ISMN-Bo 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 .
    Electronic structure of La0.7Sr0.3MnO3 thin films for hybrid organic/inorganic spintronics applications2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 11, 7292-7296 p.Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the spin injecting La0.7Sr 0.3MnO3 (LSMO) thin film contacts was investigated using photoelectron spectroscopy. Clean LSMO surfaces were obtained by annealing at 450°C in vacuum, which additionally stabilized the oxygen content determined from the exchange splitting of the Mn(3s) x-ray photoelectron spectroscopy (XPS). The valence-band structure of the films showed features of metallic LSMO. The work-function measruements of clean, annealed films yield lower values due to oxygen depletion upon annealing.

  • 36.
    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.

  • 37.
    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.

  • 38.
    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.

  • 39.
    de Jong, Michel P
    et al.
    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.
    Kanciurzewska, Anna
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Carlegrim, Elin
    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 .
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Chemical bonding in V (TCNE)x (x~2) thin-film magnets grown in situ2007In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 6Article in journal (Refereed)
    Abstract [en]

    The molecule-based magnet V (TCNE)x, with TCNE=tetracyanoethylene, x˜2, shows an exceptionally high magnetic ordering temperature of about 400 K. With the aim to shed light on the origins of the robust magnetic ordering interactions, we have characterized the chemical bonding in V (TCNE)x thin films, prepared by an in situ chemical vapor deposition method, using photoelectron spectroscopy, x-ray absorption spectroscopy (XAS), and x-ray magnetic circular dichroism (XMCD). The XAS and XMCD results were interpreted by ligand field multiplet and charge transfer multiplet calculations, which show that the V-NC bonds are characterized by a large crystal field parameter 10Dq=2.3 eV and strong ligand to metal charge transfer effects, resulting in a hybrid V (3d) -CN ground state given by 60% 3 d3 and 40% 3 d4 L, where L is a hole on the cyano ligands. © 2007 The American Physical Society.

  • 40.
    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.

  • 41.
    Doherty, Walter J
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Renouard, T.
    Institut Charles Sadron, UPR 22-CNRS, 6 Rue Boussingault, 67083 Strasbourg Cedex, France, UMR CNRS 6226, Equipe Chimie et In?nierie des Procd´s (CIP), Universit´ de Rennes 1, 263 Avenue du Gnral Leclerc, CS 74205, 35042 Rennes Cedex, France.
    Mathis, C.
    Institut Charles Sadron, UPR 22-CNRS, 6 Rue Boussingault, 67083 Strasbourg Cedex, France.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of Li-intercalated oligopyridines: A comparative study by photoelectron spectroscopy2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 126, no 9Article in journal (Refereed)
    Abstract [en]

    The role of nitrogen in the charge transfer and storage capacity of lithium-intercalated heterocyclic oligophenylenes was investigated using photoelectron spectroscopy. The development of new occupied states at low binding energies in the valence band region, as well as core level chemical shifts at both carbon and nitrogen sites, demonstrates partial charge transfer from lithium atoms to the organic component during formation of the intercalated compound. In small compounds, i.e., biphenyl and bipyridine derivatives, the position of the nitrogen heteroatom significantly affects the spacing between gap states in the Li-intercalated film, yet it has minimal effects on the charge storage capacity. In larger, branched systems, the presence of nitrogen in the aromatic system significantly enhances the charge storage capacity while the Li-N bond strength at high intercalation levels is significantly weakened relative to the nitrogen-free derivative. These observations have strong implications towards improved deintercalation processes in organic electrodes in lithium-ion batteries. © 2007 American Institute of Physics.

  • 42.
    Doherty, Walter J
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Friedlein, Rainer
    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 .
    Layer-by-layer deposition of copper phthalocyanine from aqueous solution: Molecular orientation, ordering parameters, and electronic structure2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 6, 2724-2729 p.Article in journal (Refereed)
    Abstract [en]

    Highly ordered, multilayer films composed of alternating, oppositely charged, polyionic copper phthalocyanines were prepared on HOPG [0001] substrates via layer-by-layer deposition from aqueous solution and characterized by scanning force microscopy and photoelectron spectroscopies. In films of up to four layers, individual layers alternate. Angle-resolved ultraviolet photoelectron spectra are consistent with a molecular orientation parallel to the substrate surface and indicate that structural order is reduced with film thickness © 2007 American Chemical Society.

  • 43.
    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.

  • 44.
    Fahlman, Mats
    et al.
    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 .
    Surfaces and interfaces in polymer-based electronics2002In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 500, no 1-3, 904-922 p.Article in journal (Refereed)
    Abstract [en]

    Research on electronics applications such as light-emitting devices for flat-panel displays, transistors, sensors and even solid state lasers based on conducting polymers is presently under way and in some cases has reached the stage of prototype production. The mechanisms for charge injection and conduction in these materials are being studied, as are the physics of luminescence and its quenching. Lately, research into controlling film morphology through self-organizing techniques also has gained interest. Though the present interest in conducting polymers mainly concerns the pristine semiconducting state, doped conducting polymers are also studied for potential use in many applications. In this paper, we present an overview of some of the central issues in surface and interface science in the field, as well as provide our view on what may lie ahead in the future. Specifically, the importance of metal/polymer, polymer/metal and polymer/polymer interfaces is addressed. We illustrate these using polymer-based light-emitting devices, though the same type of issues appear in other polymer-based applications such as transistors and solar cells. © 2001 Elsevier Science B.V. All rights reserved.

  • 45.
    Fauquet, C.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fredriksson, C.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Bourée, J. E.
    CNRS, Laboratoire de Meudon, Meudon, France.
    Brillaud, P.
    SMI Organometallics Division, 13 000 Marseille, France.
    Bouanah, N.
    SMI Organometallics Division, 13 000 Marseille, France.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Electronic structure of trimethylamine alane in the solid state1995In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 235, no 5-6, 528-534 p.Article in journal (Refereed)
    Abstract [en]

    The chemical and electronic structure of ultrathin molecular films of trimethylamine alane (TMAA), condensed in UHV at − 100°C, have been studied in the solid state, using both X-ray and ultraviolet photoelectron spectroscopy. The results are analyzed with the help of quantum chemical calculations at the ab initio Hartree-Fock 6-31G∗ level. Based upon the good agreement between theory and experimental, it is determined that clean, oxygen-free, condensed molecular solid films consist of the 2:1 adduct of TMAA, which was previously uncertain. In addition, based upon the electronic structure results, it is clear that the mechanism of the photodecomposition of TMAA can be explained in terms of the wavefunction of electrons photoexcited into the first unoccupied molecular orbital.

  • 46.
    Fredriksson, C.
    et al.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Bredas, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lögdlund, Michael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Theoretical studies of the aluminum/poly(p-phenylene vinylene) interface1993In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 57, no 2, 4632-4637 p.Article in journal (Refereed)
    Abstract [en]

    A molecular quantum chemical approach is used to study the aluminum on PPV (Poly(p-Phenylene Vinylene)) interface. We focus on modifications to the chemical and electronic structure of the polymer upon interaction with a submonolayer of aluminum. A model system, trans-stilbene, is taken to investigate the nature of the Al-PPV bonding. Energetically favorable conformations are then used as prototypes to study the evolution of the electronic structure as modified by the reaction with aluminum. Results at the ab initio Hartree-Fock level indicates that Al atoms react with the vinylene linkage rather than the phenyl groups at early stages of interface formation.

  • 47.
    Fredriksson, C.
    et al.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Bredas, J. L.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Lögdlund, Michael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Theoretical studies of the aluminum/trans-polyacetylene interface: Calculations of model systems and comparison to experiment1993In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 57, no 2-3, 4590-4595 p.Article in journal (Refereed)
    Abstract [en]

    The interaction between Al atoms and trans-polyacetylene has been studied quantum chemically at the ab initio Hartree-Fock level using oligomeric model systems. Investigations of the Al-polyacetylene bonding and modifications to the chemical and electronic structure of model systems for polyacetylene upon interaction with Al atoms are reported. The density-of-states is calculated for a polyene chain interacting with a pair of Al atoms. The results are discussed in relation to photoelectron spectra taken during Al deposition on an oligomeric model for polyacetylene (a diphenylpolyene with 7 C=C bonds in the polyene segment).

  • 48.
    Friedlein, R
    et al.
    Japan Adv Institute Science and Technology.
    Braun, Slawomir
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    de Jong, M P
    University of Twente.
    Osikowicz, W
    SAPA Ind.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . 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.
    Ultra-fast charge transfer in organic electronic materials and at hybrid interfaces studied using the core-hole clock technique2011In: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, ISSN 0368-2048, Vol. 183, no 1-3, 101-106 p.Article in journal (Refereed)
    Abstract [en]

    The focus of this brief review is the use of resonant photoemission in its "core-hole clock" expression for the study of two important problems relevant for the field of organic electronics: the dynamical charge transfer across hybrid organic-inorganic interfaces, and the intermolecular charge transfer in the bulk of organic thin films. Following an outline of the technique, a discussion of its applicability and a short overview of experimental results obtained thus far, two examples are used to illustrate particular results relevant for the understanding of the charge transport in organic electronic devices. First, for Fe(II)-tetraphenylporphyrin molecules on semi-metallic molybdenum disulfide substrates, the electronic coupling to the substrate and the efficiency of charge transport across the interface different for the individual molecular electronic subsystems is discussed. And second, a discotic liquid crystalline material forming columnar assemblies is used to illustrate ultra-fast intermolecular charge transfer on the order of a few femtoseconds indicating an electronic coupling between the phthalocyanine units stronger than expected from the macroscopic charge transport characteristics of the material. (C) 2011 Published by Elsevier B.V.

  • 49.
    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.

  • 50.
    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.
    Pickholz, M.
    Keil, M.
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    High intercalation levels in lithium perylene stoichiometric compounds2002In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 354, no 5-6, 389-394 p.Article in journal (Refereed)
    Abstract [en]

    Both amorphous and polycrystalline films of the aromatic hydrocarbon perylene are found to accept as high as one lithium per 3.3±0.1 carbon atoms. Phases composed of stoichiometric compounds with two, four and six lithium atoms per molecule are observed. The intercalation involves a substantial charge transfer from the lithium atoms to the molecules. Moreover, a high binding energy of the dopant-induced valence band electronic states is observed by photoelectron spectroscopy. Those observations suggest a high energy storage capacity for small- and medium-size aromatic hydrocarbons and their potential use in batteries. © 2002 Elsevier Science B.V. All rights reserved.

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