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  • 1.
    Emanuelsson, Christian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Electronic Structure and Film Morphology Studies of PTCDI on Metal/Semiconductor Surfaces2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Organic semiconductors have received increasing attention over the last decades as potential alternatives for inorganic semiconductors. The properties of these films are highly dependent on their structural order. Of special interest is the interface between the film and its substrate, since the structure of the interface and the first few layers decide the growth of the rest of the film. The interface structure is determined by the substrate/molecule interactions, the intermolecular interactions and the growth conditions.

    In this thesis, thin films of the organic semiconductor PTCDI have been studied using complementary microscopy and spectroscopy techniques on two metal-induced surface reconstructions, Ag/Si(111)-√3×√3 and Sn/Si(111)-2√3×2√3. These surfaces were chosen because they have different reactivities and surface periodicities. On the weakly interacting Ag-terminated surface, the film growth is mainly governed by the intermolecular interactions. This leads to well-ordered films that grow layer-by-layer. The interaction with the substrate is through electron charge transfer to the molecules from the substrate. This results in two different types of molecules with different electronic structure, which are identified using both STM images and PES spectra. On the more strongly interacting Sn-terminated surface the molecules adsorb in specific adsorption geometries and form 1D rows. At around 0.5 ML coverage the rows also interact with each other and form a 4√3×2√3 reconstruction and beyond one ML coverage the growth is characterized as island growth. The interaction with the substrate is mainly due to heavy electron charge transfer from the Sn atoms in the substrate to the C atoms in the imide group, but also the N atoms and the perylene core in PTCDI are involved. In these systems, the interactions with the surfaces result in new states inside the HOMO-LUMO gap, and the intermolecular interactions are dominated by O···H and O···H-N hydrogen bondings.

  • 2.
    Emanuelsson, Christian
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Johansson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Zhang, Hanmin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Delicate Interactions of PTCDI molecules on Ag/Si(111)-√3×√32018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 16, p. 164707-Article in journal (Refereed)
    Abstract [en]

    PTCDI molecules were evaporated onto a Ag/Si(111)√3×√3 surface and studied using scanning tun-resolution STM images are used to identify the delicate molecule/molecule and molecule/substrate interactions and the shapes of the molecular orbitals. The results show that the substrate/molecule interaction strongly modifies the electronic configuration of the molecules as their orbital shapes are quite different at 1 and 2 monolayer (ML) coverage. Simple models of molecular HOMO/LUMO levels and intermolecular hydrogen-bondings have been made for 1 and 2 ML PTCDI coverages to explain the STM images. Changes due to the interaction with the substrate are also found in ARUPS as extra states above the regular HOMO level at 1 ML PTCDI coverage. The ARUPS data also show that the electronic structure of the substrate remains unchanged after the deposition of molecules as the dispersion of the substrate related bands is unchanged. The changes in electronic structure ofthe molecules are discussed based on aHOMO/LUMO split.

  • 3.
    Emanuelsson, Christian
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Johansson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Zhang, Hanmin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Photoelectron spectroscopy studies of PTCDI on Ag/Si(111)-root 3 x root 32018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 4, article id 044702Article in journal (Refereed)
    Abstract [en]

    3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-root 3 x root 3 surface and studied using photoelectron spectroscopy and near edge X-ray absorption fine structure (NEXAFS). All core levels related to the imide group of the molecules showed a partial shift to lower binding energies at low coverages. In NEXAFS spectra, the first transitions to the unoccupied states were weaker at low coverages compared to thicker films. Also, extra states in the valence band between the regular highest occupied molecular orbital and the Fermi level were found at low coverages. These changes were explained by two types of molecules. Due to charge transfer from the surface, these two types have different interactions between the imide group and the substrate. As a result, one type has a partially filled lowest unoccupied molecular orbital while the other type does not. Published by AIP Publishing.

  • 4.
    Emanuelsson, Christian
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Johansson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Zhang, Hanmin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Photoelectron spectroscopy studies of PTCDI on Sn/Si(111)-2√3×2√3Manuscript (preprint) (Other academic)
  • 5.
    Emanuelsson, Christian
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Soldemo, Markus
    Johansson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Zhang, Hanmin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Scanning tunneling microscopy study of PTCDI on Sn/Si(111)-2√3×2√3Manuscript (preprint) (Other (popular science, discussion, etc.))
  • 6.
    Emanuelsson, Christian
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Zhang, Hanmin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Moons, Ellen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Johansson, Lars
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
    Scanning tunneling microscopy study of thin PTCDI films on Ag/Si(111)-root 3 x root 32017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 11, article id 114702Article in journal (Refereed)
    Abstract [en]

    3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-root 3 x root 3 surface and studied by scanning tunneling microscopy/spectroscopy and low energy electron diffraction (LEED). The growth mode was characterized as layer-by-layer growth with a single molecular unit cell in a short range order. The growth of the first two monolayers involves a molecule/substrate superstructure and a molecule/molecule superstructure. At higher coverages, the molecules in each layer were found to align so that unit cells are on top of each other. The experimentally obtained LEED pattern is described as a combination of patterns from the molecular unit cell and the molecule/substrate superstructure. The electronic structure was found to be strongly dependent on the film thickness for the first few layers: Several extra states are found at low coverages compared to higher coverages resulting in a very small pseudo gap of 0.9 eV for the first layer, which widens up to 4.0 eV for thicker films.

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