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  • 51.
    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.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Molecular parameters controlling the energy storage capability of lithium polyaromatic hydrocarbon intercalation compounds2004In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 129, no 1, p. 29-33Article in journal (Refereed)
    Abstract [en]

    One route for improving the performance of Li-based batteries is to optimize the carbon-based electrode. In order to find the best carbon-based materials, the specific roles of the molecular and solid-state contributions have to be understood. Here, the molecular contributions are analyzed. A semi-quantitative method is proposed to compare the charge storage capability of polyaromatic hydrocarbon molecules (PAHs). For planar PAHs, the ability to store electrical energy is found to be to a large extend determined by a single parameter, that is the electronic hardness (half the electronic gap) Multiplied the number of carbon atom in the molecule. A compilation of results for oligophenyls, oligoacenes and medium-size planar systems suggests trends in the dependence of the energy storage capability on the size and shape of the molecules. (C) 2003 Elsevier B.V. All rights reserved.

  • 52.
    Friedlein, Rainer
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Simpson, C. D.
    Max Planck Institute for Polymer Research, Germany.
    Watson, M. D.
    Max Planck Institute for Polymer Research, Germany.
    Jackel, F.
    Department of Physics, Humboldt University Berlin, Berlin, Germany.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Marciniak, S.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    de Jong, Michel P
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Samori, P.
    Department of Physics, Humboldt University Berlin, Berlin, Germany.
    Jönsson, Stina
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Müllen, K.
    Max Planck Institute for Polymer Research, Germany.
    Rabe, J. P.
    Department of Physics, Humboldt University Berlin, Berlin, Germany.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Electronic structure of highly ordered films of self-assembled graphitic nanocolumns2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, no 19, p. 195414-Article in journal (Refereed)
    Abstract [en]

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

  • 53.
    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.
    Suess, C.
    Pickholz, M.
    Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    The role of intermolecular polarization for the stability of lithium intercalation compounds of a- and ß-perylene2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 5, p. 2239-2245Article in journal (Refereed)
    Abstract [en]

    The charge transfer in Li-intercalation compounds of the polyaromatic hydrocarbon perylene was examined. It was found that the valence and core-level photoelectron spectroscopies characterized the bonding configuration of the alkali metal atoms. The effect of intermolecular polarization on the ionization potential of Li atoms was compensated by a screening of the Madelung energy. The data collected illustrated that the large charge transfer in the a-perylene was due to the lower ionization potential of lithium atoms.

  • 54.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Sorensen, SL
    Baev, A
    Gel'mukhanov, F
    Birgerson, J
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Murphy, C
    Agren, H
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Role of electronic localization and charge-vibrational coupling in resonant photoelectron spectra of polymers: Application to poly(para-phenylenevinylene)2004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, no 12Article in journal (Refereed)
    Abstract [en]

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

  • 55.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Sorensen, S.L.
    Sörensen, S.L., Department of Synchrotron Radiation Research, Institute of Physics, Lund University, S-221 00 Lund, Sweden.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Rosenqvist, L.
    Department of Synchrotron Radiation Research, Institute of Physics, Lund University, S-221 00 Lund, Sweden.
    Crispin, Annica
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Murphy, C.
    CDT Ltd., Cambridge CB3 0KJ, United Kingdom.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of conjugated polymers and interfaces in polymer-based electronics2003Conference paper (Refereed)
    Abstract [en]

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

  • 56.
    Friedlein, Rainer
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    von Kieseritzky, Fredrik
    Braun, Slawomir
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Linde, Christian
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Hellberg, Jonas
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Solution-processed, highly-oriented supramolecular architectures of functionalized porphyrins with extended electronic states2005Article in journal (Refereed)
    Abstract [en]

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

  • 57.
    Gadisa, Abay
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Tvingstedt, Kristofer
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Admassie, Shimelis
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lindell, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Andersson, Mats R.
    Department of Organic Chemistry and Polymer Technology, Chalmers University of Technology, Göteborg, Sweden.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Inganäs, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics . Linköping University, The Institute of Technology.
    Transparent polymer cathode for organic photovoltaic devices2006In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 156, no 16-17, p. 1102-1107Article in journal (Refereed)
    Abstract [en]

    We demonstrate a prototype solar cell with a transparent polymer cathode, and indium-tin-oxide (ITO)/poly (3, 4-ethylene dioxythiophene)-poly (styrene sulphonate) (PEDOT:PSS) anode. As an active layer, thin film of a bulk heterojunction of polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2thienyl-2′,1′3′-benzothiadiazole)] (APFO-3) and an electron acceptor molecule [6] and [6]-phenyl-C61-butyric acid methyl ester (PCBM) (1:4 wt.) was sandwiched between the two transparent polymer electrodes. The cathode is another form of PEDOT formed by vapor phase polymerised PEDOT (VPP PEDOT) of conductivity 102–103 S/cm. The cathode is supported on an elastomeric substrate, and forms a conformal contact to the APFO-3/PCBM blend. Transparent solar cells are useful for building multilayer and tandem solar cells.

  • 58.
    Greczynski, G
    et al.
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden.
    Fahlman, Mats
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Electronic structure of hybrid interfaces of poly(9,9-dioctylfluorene)2000In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 321, no 5-6, p. 379-384Article in journal (Refereed)
    Abstract [en]

    In this Letter we report the results of a study of the energy level alignment at interfaces between ultra-thin films of poly(9,9-dioctylfluorene) and AlxOy SiO2 or gold substrates, prepared under ambient (air) conditions. In all the cases, vacuum level alignment occurs, and the work function tracks that of the substrates. There is no evidence of band bending in the pristine polymer layers up to 1100 Angstrom in film thickness. Upon increasing the electrical conductivity of the polymer films by continuous doping with sodium under ultra-high-vacuum conditions, the energy levels of the polymer film gradually shift towards higher binding energies and finally become substrate independent. (C) 2000 Elsevier Science B.V. All rights reserved.

  • 59. Greczynski, G.
    et al.
    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 .
    Experimental study of poly(9,9-dioctyl-fluorene) and its interface with Li and LiF2000In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 166, no 1, p. 380-386Article in journal (Refereed)
    Abstract [en]

    The chemical and electronic structure of a new conjugated polymer, poly(9,9-dioctyl-fluorene) (PFO), has been studied by photoelectron spectroscopy. The polymer films were free of oxygen contamination (within the detection limits of photoelectron spectroscopy). X-ray and ultraviolet photoelectron spectroscopy was carried out on Li- and LiF-deposition on PFO as well as on LiF-deposition on aluminum. In the case of Li-deposition on PFO films, doping occurred resulting in the formation of polaronic charge carriers at low doping levels and bipolaronic charge carriers at high doping levels. LiF-deposition on PFO did not cause doping of the polymer films, nor did the LiF dissociate at the interface. No significant shifts in binding energy (BE) or work function occurred. LiF-deposition on sputter-cleaned aluminum showed evidence of surface dipole formation, though LiF dissociation was not detected. Al-deposition on LiF/PFO films did not cause dissociation of LiF, unlike the case in Alq3.

  • 60. Greczynski, G.
    et al.
    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 .
    Experimental study of poly(9,9-dioctyl-fluorene) and its interfaces with Li, Al, and LiF2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, no 6, p. 2407-2412Article in journal (Refereed)
    Abstract [en]

    The interaction of poly(9,9-dioctyl-fluorene) (PFO) films with Li, Al and LiF substrates was investigated by X-ray and ultraviolet photoelectron spectroscopy. The chemical and electronic structure of the interfaces were examined. The Li/PFO, LiF/PFO, LiF/Al, Al/OFO and Al/LiF/PFO interfaces were compared using Alq3.

  • 61. Greczynski, G.
    et al.
    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 .
    Hybrid interfaces of poly(9,9-dioctylfluorene) employing thin insulating layers of CsF: A photoelectron spectroscopy study2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 114, no 19, p. 8628-8636Article in journal (Refereed)
    Abstract [en]

    A number of sandwich-type interfaces were studied using x-ray and ultraviolet photoelectron spectroscopy including CsF/PFO/ Al/CsF/PFO, Al/CsF/Au, CsF/Al, CsF/AlxOy, and CsF/Au. The results indicate that the presence of aluminum is essential for dissociation.

  • 62. Greczynski, G.
    et al.
    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 .
    Johansson, N.
    Thin Film Electronics Mjärdevi, Sweden.
    Dos, Santos D.A.
    Dos Santos, D.A., Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Bredas, J.L.
    Brédas, J.L., Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Polymer interfaces studied by photoelectron spectroscopy: Li on polydioctylfluorene and Alq32000In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 363, no 1, p. 322-326Article in journal (Refereed)
    Abstract [en]

    The behavior of lithium atoms deposited on the surfaces of ultra-thin spin-coated films of poly(dioctylfluorene), and of condensed molecular solid films of tris(8-hydroxyquinoline) aluminum, have been studied through a combined experimental-theoretical approach. The Li-atoms donate charges to the organic systems, leading to doping-induced electronic states in the otherwise forbidden energy gap. The changes in the electronic structure induced by charge transfer from the Li-atoms are different in the two materials studied, and depend upon the localization of the electronic states to which the electrons are transferred. In the case of the delocalized wave functions of the p-system of poly(dioctylfluorene), at low doping levels, the added charges lead to the formation of polaron states, while at higher doping concentrations, bipolaron states are formed. In the case of the tris(8-hydroxyquinoline) aluminum, however, up to a level of three added electrons per molecule, the added electrons reside in states localized on each of the three ligands.

  • 63. Greczynski, G.
    et al.
    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 .
    Johansson, N.
    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, B-7000 Mons, Belgium.
    Dkhissi, A.
    Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Bredas, J.L.
    Brédas, J.L., Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, B-7000 Mons, Belgium.
    Electronic structure of poly(9,9-dioctylfluorene) in the pristine and reduced state2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 116, no 4, p. 1700-1706Article in journal (Refereed)
    Abstract [en]

    The electronic structure of a polymer of interest in polymer-based light emitting devices, poly(9,9-dioctyl-fluorene), was studied using a combined experimental-theoretical approach. Results were compared with those of equivalent studies of the electronic structure of two related conjugated polymers: poly(p-phenylene) and a latter-type poly (p-phenylene) (LPPP). Finally, it was shown that electrons added to the polymer system lead to the formation of polarons at low doping levels, and bipolarons at high doping levels. The energies of the polaron and bipolaron states were measured directly, and agree with the theoretical modeling of the added electrons.

  • 64. Greczynski, G.
    et al.
    Johansson, N.
    Logdlund, M.
    Lögdlund, M., ACREO AB, S-602 21 Norrköping, Sweden.
    Pettersson, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Horsburgh, L.E.
    Department of Physics, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
    Monkman, A.P.
    Department of Physics, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
    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, B-7000 Mons, Belgium.
    Bredas, J.L.
    Brédas, J.L., Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, B-7000 Mons, Belgium, Department of Chemistry, University of Arizona, 1306 E. University Blvd., Tucson, AZ 85721-0041, United States.
    Electronic structure of pristine and sodium doped poly(p-pyridine)2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 114, no 9, p. 4243-4252Article in journal (Refereed)
    Abstract [en]

    Ultraviolet spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS) were used to study the valence electronic structures of pristine and sodium doped poly (p-pyridine) (PPY). The UPS spectra were analyzed by studying the density-of-valence-states (DOVS) derived from quantum chemical calculations. The electronic band structure of the PPY chains was also theoretically investigated using the valence effective Hamiltonian (VEH) method. The theoretical approach was found to be more accurate in describing the electronic structure of PPY.

  • 65.
    Greczynski, G
    et al.
    Linkoping Univ, Dept Phys, S-58183 Linkoping, Sweden ACREO AB, Interconnect & Packaging, S-60221 Norrkoping, Sweden.
    Kugler, T
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Energy level alignment in organic-based three-layer structures studied by photoelectron spectroscopy2000In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 88, no 12, p. 7187-7191Article in journal (Refereed)
    Abstract [en]

    The alignment of energy band edges at interfaces in three-layer structures, important in polymer-based electroluminescent devices, have been studied using photoelectron spectroscopy. Careful choice of the materials allows investigation of the role of the substrate work function. These results are in agreement with the energy level diagram commonly assumed for the metal/polymer/metal structure, with the potential drop over the polymer layer being equal to the difference between the work functions of the metal contacts. Direct indication of the alignment of the electrochemical potential across the three-layer structure has been observed by photoelectron spectroscopy. (C) 2000 American Institute of Physics. [S0021-8979(00)06801-3].

  • 66. Greczynski, G.
    et al.
    Kugler, T.
    ACREO AB, Bredgatan 34, S-602 21, Norrköping, Sweden.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Photoelectron spectroscopy study of the energy level alignment at polymer/electrode interfaces in light emitting devices2001In: Current applied physics, ISSN 1567-1739, E-ISSN 1878-1675, Vol. 1, no 1, p. 98-106Article in journal (Refereed)
    Abstract [en]

    The band alignment at the interface between electroluminescent polymers and the electrodes in polymer-LEDs was studied using photoelectron spectroscopy. Chemical factors like the formation of InCl3 during conversion of precursor-PPV on ITO could be directly monitored with XPS. Films of electroluminescent polymers were studied on a range of ITO and metal electrodes with different work functions, as well as with an intermediate, electrically conducting polymer layer, using UPS. Furthermore, the study of the band alignment at polymer electrode interfaces was extended to three-layer structures: the results confirm the common assumption that the potential drop over the polymer layer in polymer LEDs is equal to the difference between the electrode work functions. © 2001 Elsevier Science B.V.

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

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

  • 68. Greczynski, G.
    et al.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Photoelectron spectroscopy of hybrid interfaces for light emitting diodes: Influence of the substrate work function2001In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 79, no 19, p. 3185-3187Article in journal (Refereed)
    Abstract [en]

    Photoelectron spectroscopy results of studies of a conjugated polymer poly(9, 9-dioctylfluorene) thin films embedded between two contacts with different work functions are reported in this work. It is demonstrated that, depending on the work function of contact material involved, the binding energy of the C(1s) core level of the polymer, changes according to the resulting built-in potential in the polymer layer. The deposition of the same metal onto a polymer surface can lead to binding energy shifts of the core-level spectra in either direction, determined by the work function of the underlying substrate. © 2001 American Institute of Physics.

  • 69. Greczynski, G.
    et al.
    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 .
    An experimental study of poly(9,9-dioctyl-fluorene) and its interfaces with Al, LiF and CsF2001In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 175-176, p. 319-325Article in journal (Refereed)
    Abstract [en]

    Sandwich-style interfaces of Al/LiF/poly(9,9-dioctyl-fluorene) and Al/CsF/poly(9,9-dioctyl-fluorene) have been studied using X-ray and ultraviolet photoelectron spectroscopy. The polymer films were free of oxygen contamination (within the detection limits of photoelectron spectroscopy). In the case of LiF-deposition on poly(9,9-dioctyl-fluorene) films, doping did not occur, nor did the LiF dissociate upon Al-deposition. No significant shifts in a binding energy of the core levels, nor any changes in the work function were detected. However, for the Al/LiF/poly(9,9-dioctyl-fluorene) interface, there was no degradation of the p-electronic structure, unlike the case for Al deposited directly unto poly(9,9-dioctyl-fluorene). For the Al/CsF/poly(9,9-dioctyl-fluorene) interface, the CsF dissociated upon Al-deposition, with the Cs likely n-doping, the polymer at the interface. When deposited onto an Al surface, CsF also were found to dissociate at the interface but remaining in the CsF form away from the Al surface. © 2001 Elsevier Science B.V.

  • 70. Greczynski, G.
    et al.
    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 .
    Hybrid interfaces in polymer-based electronics2001In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 121, no 1-3, p. 1625-1628Article in journal (Refereed)
    Abstract [en]

    Sandwich-style interfaces of Al/LiF/poly(9,9-dioctyl-fluorene) and A1/CsF/poly(9,9-dioctyl-fluorene) have been studied using X-ray and ultraviolet photoelectron spectroscopy. In the case of LiF-deposition on poly(9,9-dioctyl-fluorene) films, doping did not occur, nor did the LiF dissociate upon Al-deposition. No significant shifts in binding energy of the core levels, or any changes in the work function were detected. However, for the Al/LiF/poly(9,9-dioctyl-fluorene) interface, there was no degradation of the p-electronic structure, unlike the case for Al deposited directly unto poly(9,9-dioctyl-fluorene). For the Al/CsF/poly(9,9-dioctyl-fluorene) interface, the CsF dissociated upon Al deposition, with the Cs likely n-doping the polymer at the interface. When deposited onto an Al surface, CsF also was found to dissociate at the interface but remaining in the CsF form away from the Al surface. Vacuum level alignment occurs for poly(9,9-dioctyl-fluorene) films spun onto 'metal' substrates. The hole-injection barrier in poly(9,9-dioctyl-fluorene)-based LEDs is hence determined by the difference between anode work function and the polymer ionization potential.

  • 71.
    Guo, J.-H.
    et al.
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Såthe, C
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Yang, L.
    Luo, Y
    Ågren, H.
    Xing, K.
    Johansson, N.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Daik, R
    Durham University.
    Feast, W. J.
    Durham University.
    How the phenyle rings (benszene) act as builing blocks in conjugated polymers1998Report (Other academic)
  • 72.
    Guo, J.-H.
    et al.
    Uppsala University.
    Magnuson, Martin
    Uppsala University.
    Såthe, C.
    Uppsala University.
    Nordgren, J.
    Uppsala University.
    Yang, L.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Luo, Y.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Ågren, H.
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Xing, K. Z.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Johansson, N.
    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.
    Daik, R.
    Durham University.
    Feast, W. J.
    Durham University.
    Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s1998In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 108, no 14, p. 5990-5996Article in journal (Refereed)
    Abstract [en]

    The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer π band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds.

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  • 73.
    Jakobsson, Fredrik L. E.
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Lindell, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Kanciurzewska, Anna
    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, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Berggren, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Towards all-plastic flexible light emitting diodes2006In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 433, no 1-3, p. 110-114Article in journal (Refereed)
    Abstract [en]

    All-plastic light emitting diodes require the design and fabrication of low work function plastic electrodes. Here, we show that the work function of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT-PSS) can be decreased from 4.8 eV to 3.9 eV by surface reaction with the strong electron-donor tetrakis(dimethylamino)ethylene (TDAE). The surface modification was characterized by photoelectron spectroscopy and optical spectroscopy. The low work function plastic electrode was used in a first prototype for all-plastic light emitting diodes.

  • 74.
    Johansson, N.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Osada, T.
    Sumitomo Chem Co Ltd, Japan.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Parente, V.
    Mons University, Belgium.
    dos Santos, D. A.
    Mons University, Belgium.
    Crispin, Xavier
    Mons University, Belgium.
    Bredas, J. L.
    Mons University, Belgium.
    Electronic structure of tris(8-hydroxyquinoline) aluminum thin films in the pristine and reduced states1999In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 111, no 5, p. 2157-2163Article in journal (Refereed)
    Abstract [en]

    The electronic structure of tris(8-hydroxyquinoline) aluminum (Alq(3)) has been studied in the pristine molecular solid state as well as upon interaction (doping) with potassium and lithium. We discuss the results of a joint theoretical and experimental investigation, based on a combination of x-ray and ultraviolet photoelectron spectroscopies with quantum-chemical calculations at the density functional theory level. Upon doping, each electron transferred from an alkali metal atom is stored on one of the three ligands of the Alq(3) molecule, resulting in a new spectral feature (peak) in the valence band that evolves uniformly when going from a doping level of one to three metal atoms per Alq(3) molecule. (C) 1999 American Institute of Physics. [S0021-9606(99)50628-4].

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  • 75.
    Jönsson, Stina
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Birgerson, J.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Greczynski, Grzegorz
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Denier van der Gon, A.W.
    Denier van der Gon, A.W., Faculty of Applied Physics, Eindhoven University of Technology, Eindhoven, Netherlands.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    The effects of solvents on the morphology and sheet resistance in poly(3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT–PSS) films2003In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 139, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

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

  • 76.
    Jönsson, Stina
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Carlegrim, Elin
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhang, Fengling
    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.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Photoelectron spectroscopy of the contact between the cathode and the active layers in plastic solar cells: the role of LiF2005In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 44, no 6A, p. 3695-3701Article in journal (Refereed)
    Abstract [en]

    The surfaces and electrode interfaces of a polymer blend used in prototype solar cells have been characterized with photoelectron spectroscopy. The polymer blend in question is a 1:4 mixture of APFO-3:PCBM. Based on surface analysis of the pristine film we can conclude that the surface of the blend is a 1:1 mixture of APFO-3 and PCBM. The electrode systems studied are the widely used Al and Al/LiF contacts. LiF prevents formation at the Al/organic interface of Al-organic complexes that destroy the π-conjugation. In addition to this, there are two other beneficial, thickness dependent, effects. Decomposition of LiF occurs for thin enough layers in which the LiF species are in contact with both the organic film and the Al atoms, which creates a low workfunction contact. For thicker (multi)layers, the dipole formed at the LiF/organic interface is retained as no decomposition of the LiF occurs upon Al deposition.

  • 77.
    Jönsson, Stina
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    de Jong, Michel P
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Groenendaal, L.
    R&D Materials, Chemistry Department, AGFA-Gevaert NV, Mortsel, Belgium.
    Salaneck, William R
    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.
    Phenyl-capped EDOT trimer: its chemical and electronic structure and its interface with aluminum2003In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, no 39, p. 10793-10800Article in journal (Refereed)
    Abstract [en]

    The chemical and electronic properties of a phenyl-capped 3,4-(ethylenedioxy)thiophene trimer (EDOT trimer) and its interface formation with aluminum have been studied. Thin EDOT trimer films were prepared on clean gold substrates through in-situ vapor deposition. Aluminum was deposited stepwise on top of the EDOT trimer, and the initial stages of interface formation were investigated by photoelectron spectroscopy. The organic/metal interface formed was not completely abrupt; some degree of diffusion of aluminum into the EDOT trimer film occurred. The aluminum atoms preferentially react with the α-position of the trimer (C−S carbon atoms) forming covalent bonds. The formation of these covalent bonds causes a break in the π-conjugation of the system due to the introduction of sp3 defects. The charge density also is somewhat redistributed within the oligomer as a whole, mainly affecting the neighboring atoms:  sulfur and β-position of the trimer (C=C−O carbon atoms). Once the C−S carbon sites are saturated, the aluminum instead reacts with the less favorable carbon atom of the ethylene bridge (C−O−C carbons). Worth noting is the decrease in work function from 5.2 eV for sputter cleaned gold to 4.1 eV upon deposition of the EDOT trimer. Our results have several implications for organic electronics. The sp3 defects introduced by the aluminum−EDOT contacting will influence the charge injection into the material across the EDOT trimer/aluminum interface negatively. The change in work function could potentially be used to modify gold contacts for electron injection into molecules with low electron affinity.

  • 78.
    Jönsson, Stina
    et al.
    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.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Photoemission of Alq3 and C60 films on Al and LiF/Al substrates2005In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 98, no 1, p. 14901-14907Article in journal (Refereed)
    Abstract [en]

    Photoemission studies of thin films of Alq3 and C60 deposited on Al and LiF/Al substrates have been performed in order to deduce the interactions of the organic films with the substrates. For all cases there is evidence of strong interaction resulting in the formation of interfacial dipoles. Attempts to explain the origin of these interfacial dipoles and the type of interface formed in each case have been done through analysis of the valence electronic structure and core levels of the materials. The origin of the interfacial dipoles is mainly covalent interaction when the organic films are deposited on Al substrates, and charge transfer between the organic molecules and the metal through the LiF sandwich layer when the organic films are deposited on LiF/Al substrates. For thick-enough LiF films, however, there is no interaction between the organic films and the substrates. In no case does the LiF dissociate, unlike what is found for the reverse order of deposition. Two charge-transfer-induced gap states are found for (sub)monolayer films of Alq3 deposited on LiF/Al. We propose that the formation of two gap states corresponds to negatively charged fac-Alq3.

  • 79.
    Jönsson, Stina
    et al.
    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.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Spectroscopy of ethylenedioxythiophene-derived systems: from gas phase to surfaces and interfaces found in organic electronics2004In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 137-140, p. 805-809Article in journal (Refereed)
    Abstract [en]

    Two relevant topics within the field of organic electronics have been studied with photoelectron spectroscopy. The organic material used is the successful polymer blend PEDOT-PSS. The first issue relates to the conductivity of organic materials. A known procedure (specific solvent-mixture) for improving the conductivity of PEDOT-PSS has been studied. The mechanisms behind the enhanced conductivity were shown to be due to higher PEDOT content at the surface. The other issue has to do with metal contacting of organic materials. Aluminum/PEDOT-PSS interfaces were studied. The formation of interfacial species was deduced with the aid of model molecules. We can conclude that it is mainly the PSS part that reacts with aluminum. Due to different surfaces in standard PEDOT-PSS and solvent-treated PEDOT-PSS, different interfaces are formed in the two cases.

  • 80.
    Jönsson, Stina
    et al.
    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.
    Fahlman, Mats
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    X-ray photoelectron spectroscopy study of the metal/polymer contacts involving aluminum and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) derivatives2003In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 18, no 5, p. 1219-1226Article in journal (Refereed)
    Abstract [en]

    The contact formed between aluminum and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) (PEDOT-PSS) derivatives was studied using x-ray photoelectron spectroscopy. The aluminum/PEDOT-PSS contact contains an interfacial layer formed by chemical reactions between aluminum and mainly poly(styrenesulfonic acid) (PSSH). These chemical interactions were studied with the help of model systems (PSSH, benzenesulfonic acid, and sodium benzenesulfonate). The preferred reaction site of aluminum is the SO3 and SO3H+ groups of the PSS chains, giving rise to C-S-Al(-O) and C-O-Al species. The resulting contact formed consists of an insulating aluminum/PSS layer and a thin region of partially dedoped PEDOT-PSS. There is significant aluminum diffusion into films of the highly conducting form of PEDOT-PSS that have substantially less PSS at the surface. Hence, no (thick) aluminum/PSS layer is formed in this case, though the PEDOT chains close to the aluminum contact will still be partially dedoped as for the aluminum/PEDOT-PSS case.

  • 81. Keil, M.
    et al.
    Samori, P.
    Samorí, P., Department of Physics, Humboldt University Berlin, Invalidenstrasse 110, D-10115 Berlin, Germany.
    Dos, Santos D.A.
    Dos Santos, D.A., Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Birgerson, J.
    Friedlein, Rainer
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Dkhissi, A.
    Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium.
    Watson, M.
    Max-Planck-Institut for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
    Mullen, K.
    Müllen, K., Max-Planck-Institut for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
    Bredas, J.L.
    Brédas, J.L., Université de Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium, Department of Chemistry, University of Arizona, Tucson, AZ 85721, United States.
    Rabe, J.P.
    Department of Physics, Humboldt University Berlin, Invalidenstrasse 110, D-10115 Berlin, Germany.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    High levels of alkali-metal storage in thin films of hexa-peri-hexabenzocoronene2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 116, no 24, p. 10854-10860Article in journal (Refereed)
    Abstract [en]

    The results of the doping of molecular solid films of the medium-sized aromatic hydrocarbon hexa-peri-hexabenzocoronene (HBC), using lithium or sodium atoms were presented. The evolution of the valence band electronic structure was monitored by x-ray photoelectron spectroscopy and studied by ultraviolet photoelectron spectroscopy. Results indicated that n-doping depended on the type of alkali-metal atom employed and on the molecular order of the film. The smaller Li ion was found to have a stronger influence on the electronic structure than Na ions. These results revealed the potential use of the graphene materials in lithium-ion batteries with a high charge-storage capacity.

  • 82. Keil, M
    et al.
    Samori, P
    dos Santos, DA
    Kugler, T
    Stafström, Sven
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Computational Physics .
    Brand, JD
    Mullen, K
    Bredas, JL
    Rabe, JP
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Influence of the morphology on the electronic structure of hexa-peri-hexabenzocoronene thin films2000In: JOURNAL OF PHYSICAL CHEMISTRY B, ISSN 1089-5647, Vol. 104, no 16, p. 3967-3975Article in journal (Refereed)
    Abstract [en]

    Ultrathin films of hexa-peri-hexabenzocoronene (HBC), prepared in ultrahigh vacuum by sublimation and studied using a combination of atomic force microscopy, X-ray absorption spectroscopy, and photoelectron spectroscopy were interpreted with the help of results of quantum chemical calculations. The important role of the nature of the surface of the substrate as well as the effect of postdeposition annealing on the morphology and the subsequent electronic structure were studied. In particular, on the (0001) surfaces of highly oriented pyrolitic graphite (HOPG) or molybdenum disulfide (MoS2), there is a high degree of molecular order induced by the crystal structure of the substrate surface. When deposited at room temperature on HOPG, the molecules are epitaxially ordered, while crystals from the epitaxially ordered films nucleate and grow during heating. On oxidized silicon(001) or polycrystalline gold surfaces, only totally disordered molecular solid films are formed. The epitaxial films assume a layered structure and exhibit a graphite-like electronic structure. In particular, the relationship between electronic structure and topology is discussed. The results of these studies indicate methods for the preparation of the crystalline seeds to molecular wires.

  • 83.
    Kim, J.S.
    et al.
    Cavendish Laboratory, Dept. Phys., Univ. Cambridge, M., Cambridge, United Kingdom.
    Lagel, B.
    Lägel, B., Department of Physics, Robert Gordon University, Aberdeen, United Kingdom.
    Moons, E.
    Cavendish Laboratory, Dept. Phys., Univ. Cambridge, M., Cambridge, United Kingdom.
    Johansson, N.
    Baikie, I.D.
    Department of Physics, Robert Gordon University, Aberdeen, United Kingdom.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Friend, R.H.
    Cavendish Laboratory, Dept. Phys., Univ. Cambridge, M., Cambridge, United Kingdom.
    Cacialli, F.
    Cavendish Laboratory, Dept. Phys., Univ. Cambridge, M., Cambridge, United Kingdom.
    Kelvin probe and ultraviolet photoemission measurements of indium tin oxide work function: a comparison2000In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 111, p. 311-314Article in journal (Refereed)
    Abstract [en]

    We report a comparison of the work functions of thin films of indium tin oxide (ITO), carried out by means of ultraviolet photoelectron spectroscopy (UPS) and by measurements of the contact potential difference with respect to a gold reference electrode (Kelvin probe (KP) method). We investigated commercially available ITOs both 'as-received', and after certain surface treatments, such as oxygen plasma. First, we find measurable discrepancies between KP values measured with three different instruments, and between the KP and the UPS values. Secondly, and unexpectedly, we find that the KP, although more sensitive than UPS, does not detect certain differences between ITOs with different surface treatments. We discuss the results in view of the different environments in which the measurements are carried out (UHV for the UPS and air/Ar for the Kelvin method), of the effects which may be induced by the high-energy photon irradiation in the UPS measurement, and of the stability of the gold probe work function in gas ambient. We conclude that UPS is better-suited for absolute work function determination, although KP remains a convenient and inexpensive tool for fast screening of contact potential differences.

  • 84. Kugler, T
    et al.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry .
    Chemical species at polymer/ITO interfaces: consequences for the band alignment in light-emitting devices2000In: Comptes rendus de l'Académie des sciences. Série IV, Physique, astrophysique, ISSN 1296-2147, E-ISSN 1878-5557, Vol. 1, no 4, p. 409-423Article in journal (Refereed)
    Abstract [en]

    The influence of chemical species present at the interface between the electroluminescent polymer and the ITO electrode in light-emitting devices on the band edge energies of overlayers of semiconducting conjugated polymers has been studied using photoelectron spectroscopy. The formation of InCl3 during the conversion of precursor-PPV on ITO was directly monitored with XPS. Ultrathin films of poly(bis-(2-dimethyloctylsilyl)-1,4-phenylenevinylene) were studied directly on ITO, as well as with an intermediate layer of an electrically conducting polymer using UPS. The initial work function of the ITO was varied chemically from 4.4 eV to 4.8 eV. In addition, the work function of ITO was changed in situ, within a given sample, by exposure to X-rays. For the polymer spin-coated directly on ITO, the vacuum levels are aligned. With the electrically conducting polymer blend, poly(3,4-ethplenedioxythiophene) doped with poly(4-styrene sulfonate) spin-coated on ITO, the Fermi levels are aligned, as expected. Therefore, with a conducting polymer blend intermediate layer between the polymer and the ITO, the polymer bands align to the vacuum level of the conducting polymer blend on ITO, and the barrier to hole injection into the polymer is determined by the work function of the conducting polymer blend instead of the work function of the ITO. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

  • 85. Kuritka, I.
    et al.
    Negri, F.
    Brancolini, G.
    Suess, C.
    Salaneck, William R
    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 .
    Lithium intercalation of phenyl-capped aniline dimers: A study by photoelectron spectroscopy and quantum chemical calculations2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 38, p. 19023-19030Article in journal (Refereed)
    Abstract [en]

    Structural and electronic properties of pristine and lithium-intercalated, phenyl-capped aniline dimers as a model for the lithium-polyaniline system have been studied by photoelectron spectroscopy and quantum chemical calculations. It was found that the electronic structure of reduced and oxidized forms of oligoanilines is only weakly affected by isomerism. Upon intercalation, charge transfer from the Li-atoms is remarkable and highly localized at N-atomic sites, where configurations are energetically favored in which both N atoms of the dimers are bound to Li atoms. Conversion of nitrogen sites is different for the two forms of aniline dimers and incomplete up to high intercalation levels, indicating a pronounced role of solid-state effects in the formation of such compounds. © 2006 American Chemical Society.

  • 86.
    Lazzaroni, R.
    et al.
    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.
    Chtaïb, M.
    Laboratoire Interdépartemental de Spectroscopie Electronique, Facultés Universitaires Notre-Dame de la Paix, Namur, Belgium.
    Snauwaert, P.
    Laboratoire Interdépartemental de Spectroscopie Electronique, Facultés Universitaires Notre-Dame de la Paix, Namur, 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.
    Uvdal, Kajsa
    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.
    Electronic Structure of Metal/Polymer Interfaces: aluminum on Conjugated Polymers1991In: Metallized Plastics 2: fundamental and applied aspects / [ed] Kashmiri Lal Mittal, Springer, 1991, p. 199-212Chapter in book (Other academic)
    Abstract [en]

    Aluminum has been deposited on two types of conjugated polymers, polyalkylthiophene and polyaniline. The polymers were in the undoped, neutral form which possesses semiconducting properties. The chemical structure of the metal/polymer interface has been investigated by X-ray and UV photoelectron spectroscopy. Core level spectra indicate that aluminum reacts with the sulfur atom of the polythiophene chain, strongly perturbing the π-electron system. In the case of polyaniline, the interaction with the metal depends on the oxidation state of the polymer. UPS data, combined with the results of band structure calculations, are interpreted in terms of the Al-induced modifications of the π-electron system.

  • 87.
    Lazzaroni, R.
    et al.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons-Hainaut, Mons, Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons-Hainaut, Mons, Belgium.
    Dannetun, Per
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons-Hainaut, Mons, Belgium.
    Fredriksson, C.
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons-Hainaut, Mons, Belgium.
    Stafström, Sven
    Service de Chimie des Matériaux Nouveaux, Département des Matériaux et Procédés, Université de Mons-Hainaut, Mons, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    The chemical and electronic structure of the interface between aluminum and conjugated polymers1994In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 39, no 2, p. 235-244Article in journal (Refereed)
    Abstract [en]

    The chemical and electronic structure of the interface between aluminum and several proto-typical conjugated systems is investigated with a combined experimental and theoretical approach. The experiments consists of following the evolution of the polymer surface during the early stages of aluminum deposition, with X-ray and Ultraviolet Photoelectron Spectroscopies (XPS, UPS). In parallel, quantum chemical calculations are performed on model oligomer systems interacting with isolated Al atoms. Aluminum is found to interact strongly with the polymer chain. New covalent Al-carbon bonds are formed along the polymer backbone; the chain geometry is deeply modified and the π electron conjugation can be dramatically reduced.

  • 88.
    Lazzaroni, R.
    et al.
    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.
    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.
    Uvdal, Kajsa
    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.
    Electronic structure of the aluminum/polythiophene interface: A joint experimental and theoretical study1991In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 43, no 1-2, p. 3323-3328Article in journal (Refereed)
    Abstract [en]

    Not Available.

  • 89.
    Lazzaroni, R.
    et al.
    Service de Chimie des Maririaux Nouveaux Département des Matériaux et Procédés Universitt de Mons-Hainaw, Mons, Belgium.
    Fredriksson, C.
    Service de Chimie des Maririaux Nouveaux Département des Matériaux et Procédés Universitt de Mons-Hainaw, Mons, Belgium.
    Brédas, J. L.
    Service de Chimie des Maririaux Nouveaux Département des Matériaux et Procédés Universitt de Mons-Hainaw, Mons, Belgium.
    Dannetun, Per
    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.
    The Chemical and Electronic Structure of Metal/Conjugated Polymer Interfaces: A Joint Theoretical and Experimental Study1993In: Intrinsically Conducting Polymers: An Emerging Technology / [ed] M. Aldissi, Springer Netherlands, 1993, p. 135-146Chapter in book (Refereed)
    Abstract [en]

    We investigate the interface between aluminum and several prototypical conjugaced systems wich a combined experimental and theoretical approach. The experiments consist of following the evolution of the polymer surface during the early stages of aluminum deposition, with X-ray and Ultraviolet Photoe!ectron Spectroscopies (XPS, UPS). In parallel, we perform quantum chemical calculacions on mode! oligomer systems interacting with one to four Al atoms. Aluminum is found to internet strongly with the polymer chain. Al·carbon covalenc boods an: formed along the polymer backbone; the chain geomeuy is deeply modified and the π electron conjugation can be dramatically reduced.

  • 90.
    Lazzaroni, R.
    et al.
    Service de Chimie des Matériaux Nouveaux Centre de Recherche en Electronique et Photonique Moléculaires Université de Mons-Hainaut, Mons, Belgium.
    Lögdlund, Michael
    Service de Chimie des Matériaux Nouveaux Centre de Recherche en Electronique et Photonique Moléculaires Université de Mons-Hainaut, Mons, Belgium.
    Calderone, A.
    Service de Chimie des Matériaux Nouveaux Centre de Recherche en Electronique et Photonique Moléculaires Université de Mons-Hainaut, Mons, Belgium.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux Centre de Recherche en Electronique et Photonique Moléculaires Université de Mons-Hainaut, Mons, Belgium.
    Dannetun, Per
    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.
    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.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Chemical and electronic aspects of metal/conjugated polymer interfaces: Implications for electronic devices1995In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 71, no 1-3, p. 2159-2162Article in journal (Refereed)
    Abstract [en]

    The chemical nature and the electronic structure of metal/conjugated polymer interfaces are investigated in the context of polymer-based light-emitting diodes. We consider the interaction of low-workfunction metals (Al, Ca) with the surface of conjugated polymers or model oligomer molecules with a combined experimental and theoretical approach. The early stages of the interface formation are followed with X-ray and ultraviolet photoelectron spectroscopies and the experimental data are compared to the results of quantum chemical calculations. The reactions of Al and Ca with the organic surface are found to be fundamentally different: while the former forms new covalent bonds onto the polymer backbone, the latter tends to dope the conjugated system. Both types of reaction are expected to modify drastically the electronic properties of the polymer semiconductor.

  • 91.
    Lindell, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Braun, Slawomir
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    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 metal-organic and organic-organic interfaces with Alq3 and NTCDAManuscript (preprint) (Other academic)
    Abstract [en]

    The energy level alignment behavior of the widely used materials tris-(8-hydroxyquinoline)aluminum (Alq3) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) is investigated. The Integer Charge Transfer (ICT) model is successfully used to predict their overall behavior at weakly-interacting hybridorganic and organic-organic interfaces, including NTCDA/Alq3 bilayers. The EICT- of NTCDA is measured to be 4.35 eV and the EICT+ of Alq3 is found to be 4.3 eV. The Alq3 films furthermore feature an interface dipole in absence of charge transfer due to the intrinsic dipole of the molecule and ordering effects.

  • 92.
    Lindell, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Burquel, A.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, 5-7000 Mons, Belgium.
    Jakobsson, Fredrik
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Lemaur, V.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, 5-7000 Mons, Belgium.
    Berggren, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Lazzaroni, R.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, 5-7000 Mons, Belgium.
    Cornil, J.
    Service de Chimie des Matériaux Nouveaux, Université de Mons-Hainaut, Place du Parc 20, 5-7000 Mons, Belgium.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Transparent, plastic, low-work-function poly(3,4-ethylenedioxythiophene) electrodes2006In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 18, no 18, p. 4246-4252Article in journal (Refereed)
    Abstract [en]

    Novel applications for flexible electronics, e.g., displays and solar cells, require fully flexible, transparent, stable, and low-work-function electrodes that can be manufactured via a low-cost process. Here, we demonstrate that surface chemistry constitutes a route to producing transparent low-work-function plastic electrodes. The work function of the conducting polymer poly(3,4-ethylenedioxythiophene)-tosylate, or PEDOT-Tos, is decreased by submonolayer surface redox reaction with a strong electron donor, tetrakis-(dimethylamino)ethylene (TDAE), allowing it to reach a work function of 3.8 eV. The interface formed between TDAE and PEDOT is investigated in a joint experimental and theoretical study using photoelectron spectroscopy and quantum chemical calculations. © 2006 American Chemical Society.

  • 93.
    Lindell, Linda
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    de Jong, Michel P
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Lazzaroni, R
    Berggren, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Characterization of the interface dipole at the paraphenylenediamine-nickel interface: A joint theoretical and experimental study2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 8, p. 84712-Article in journal (Refereed)
    Abstract [en]

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

  • 94.
    Lindell, Linda
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Jakobsson, Fredrik
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Osikowicz, Wojciech
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Andersson, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Salaneck, William R
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry.
    Berggren, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Cornil, Jerome
    Crispin, Xavier
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Towards Transparent Inorganic and Plastic Low-Workfunction Electrodes2005In: MRS Fall Meeting,2005, 2005Conference paper (Refereed)
  • 95.
    Lindell, Linda
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Unge, Mikael
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Osikowicz, Wojciech
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Stafström, Sven
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics . Linköping University, The Institute of Technology.
    Salaneck, William R
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Crispin, Xavier
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    de Jong, Michael P
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry . Linköping University, The Institute of Technology.
    Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 16, p. 163302-1-163302-3Article in journal (Refereed)
    Abstract [en]

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

  • 96.
    Luo, Y.
    et al.
    Theoretical Chemistry, Roy. Inst. of Technology, S-10044, Stockholm, Sweden.
    Agren, H.
    Ågren, H., Theoretical Chemistry, Roy. Inst. of Technology, S-10044, Stockholm, Sweden.
    Keil, M.
    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 .
    A theoretical investigation of the near-edge X-ray absorption spectrum of hexa- peri -hexabenzocoronene2001In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 337, no 1-3, p. 176-180Article in journal (Refereed)
    Abstract [en]

    The near-edge X-ray absorption spectrum of hexa-peri-hexabenzocoronene has been simulated by density functional theory techniques using transition state and full core hole potentials. The total spectrum is found to be a composition of multiple structure in the subspectra of the symmetry unique carbons, rather than by chemically shifted single p* transitions. This quite 'fullerene-like' behavior, with only minor reminiscence of either graphite or benzene spectral features, is used to argue that long-range effects must be important to build up the dominating single excitonic p* feature in graphite. © 2001 Elsevier Science B.V.

  • 97.
    Lögdlund, Michael
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Mons, Belgium.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Fredriksson, C.
    Ecole Polytechnique de Montréal, Centre de Recherche Appliquée Sur les Polymères (CRASP), Département de Génie Chimique, Case Postale 6079, Succursale A, Montréal, Québec, H3C 3A7 Canada.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Mons, Belgium.
    Theoretical and experimental studies of the interaction between sodium and oligothiophenes1996In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 53, no 24, p. 16327-16333Article in journal (Refereed)
    Abstract [en]

    Quantum-chemical calculations and ultraviolet photoelectron spectroscopy (UPS) measurements have been performed in order to study the interaction between sodium and oligothiophenes, with a focus on the origin of experimentally observed relaxation energy effects in alkali-metal-doped conjugated molecules. Upon doping of a -sexithienylene (α-6T) with sodium atoms, (1) a broad feature appears in the valence band, in an energy region corresponding to the band gap in pristine α-6T, and (2) certain structural features in the valence band shift towards lower binding energies in the doped material. In particular, upon doping, a structural peak related to electronic levels mainly localized to the sulfur and b-carbon atoms destabilizes to an energy corresponding to that of the valence-band edge in pristine α-6T. The results of ab initio Hartree-Fock and local-spin-density calculations on α-trithienylene and bithiophene are consistent with the experimental data, and allow for an assignment of these destabilization effects in terms of initial-state relaxations. We stress that similar destabi-lization effects, reported for other alkali-metal-doped conjugated systems, had previously been proposed to be associated with final-state electronic screening, i.e., a dynamic artifact within the UPS measurements; this is in contradiction to the results of our ab initio theoretical studies. Our present results show that all structural features in the UPS data are contained in the results of sufficiently complete quantum chemical calculations.

  • 98.
    Lögdlund, Michael
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Mons, Belgium.
    Dannetun, Per
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology. Groupe de Physique des Solides, place Jussieu, 75251 Paris Cedex 05, France.
    Fredriksson, C.
    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.
    Brédas, J. L.
    Service de Chimie des Matériaux Nouveaux, Centre de Recherche en Electronique et Photonique Moléculaires, Université de Mons-Hainaut, Mons, Belgium.
    Theoretical study of the interaction between sodium and oligomers of poly(p-phenylenevinylene) and poly(p-phenylene)1994In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 67, no 1-3, p. 141-145Article in journal (Refereed)
    Abstract [en]

    The semi-empirical Austin Model 1 and the non-empirical pseudo-potential valence effective Hamiltonian (VEH) methods as well as the local spin density (LSD) approximation technique have been applied to the investigation of the doping-induced electronic and geometrical changes in some conjugated molecules related to poly(p-phenylene) and poly(p-phenylenevinylene) (PPV): biphenyl, stilbene and a phenyl-capped dimer of PPV. The theoretical results are compared with experimental valence band spectra, as recorded by ultraviolet photoelectron spectroscopy (UPS). The experimental UPS studies show that two ingap states are detected upon doping with alkali metals. The energy splitting between the two in-gap states increases as the molecule size decreases. The results of the LSD calculations agree very well with the experimental results, while the VEH method overestimates the energy splitting for the small molecules. The LSD modelling also indicates a destabilization of several high binding energy valence levels, due to the presence of counter-ions, in agreement with experiment.

  • 99.
    Lögdlund, Michael
    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.
    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, Faculty of Science & Engineering.
    Sprangler, C. W.
    Deartment of Chemistry, Nothern lllinois University, USA.
    Brédas, J. L.
    lService de Chimie des Materiaux Nouveaux, Université de Mons-Hainaut, Belgium.
    Salaneck, William R.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Experimental and Theoretical Studies of the Interaction of Metals with Polymer Surfaces: A Case Study of the Use of a Model Molecular System to Study the Nature of Charge Storage in Short Polyenes1994In: Frontiers of Polymers and Advanced Materials / [ed] Paras N Prasad, Springer-Verlag New York, 1994, p. 369-382Chapter in book (Refereed)
    Abstract [en]

    The electronic and geometric changes in polyenes induced by doping with sodium have been studied using X-ray and Ultraviolet Photoeclectron Spectroscopy, and quantum chemical calculations. The molecular geometry changes induced by doping have been studied using the semiempirical Austin Model 1 method, the results of which has served as input parameters for Valence Effective Hamiltonian band structure calculations, which are compared with the experimental density-of-states data. The molecules studied are members of a series of diphenylpolyenes with 4, 5, 6 ir 7 C=C double bonds in the polyene part of the molecule, i.e., the series DPx, with x = 4, 5, 6 or 7. Since the frontier orbitals of the diphenylpolyenes are localized mostly on the polyene chain portion of the molecule, there is a high degree of separations in energy of the phenyl and polyene parts of the π-system. Hence, many chemical and electronic properties of diphenylpolyenes are similar to those of (at least short chain) trans-polyacerylene. The present doping results indicate the charge is stored in short polyenes in the form of two confined solitons per molecule.

  • 100.
    Lögdlund, Michael
    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.
    Sjögren, B.
    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.
    Fredriksson, C.
    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.
    The electronic structure of α,ω-diphenyltetradecaheptaene, a model molecule for polyacetylene, as studied by photoelectron spectroscopy1992In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 51, no 1, p. 187-195Article in journal (Refereed)
    Abstract [en]

    The advantages of using model systems for spectroscopic studies of conjugated polymers and interface formation, as well as for charge-induced electronic and geometric structural changes, are discussed. The electronic structure of a diphenylpolyene, α,ω-diphenyltetradecaheptaene, or DP7, is an example of a model molecular system studied using X-ray and Ultraviolet Photoelectron Spectroscopy, XPS, and UPS. The spectra are interpreted with the help of the results from MNDO, VEH and INDO/S-CI quantum chemical calculations. The frontier orbitals of DP7 are localized mostly on the polyene chain portion of the molecule, resulting in a high degree of separation of the phenyl and polyene parts of the π-system. The INDO calculations show two regions of shake-up features corresponding to a benzene-like part and a polyene-like part. The most important individual shake-up transitions, which contribute to the two observed shake-up spectral features, involve one-electron redistributions separable into contributions from the polyene chain and from the phenyl groups. The analysis indicates the extent to which many chemical and electronic properties of DP7 are expected to be similar to those of (at least short chain) trans-polyacetylene.

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