AVS 51st International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF+EM-WeM

Paper OF+EM-WeM10
Planar Molecular Networks Built by 1D and 2D Polymerization

Wednesday, November 17, 2004, 11:20 am, Room 304C

Session: Molecular and Organic Films and Devices - Electronics
Presenter: M. Stöhr, University of Basel, Switzerland
Authors: M. Stöhr, University of Basel, Switzerland
M. Wahl, University of Basel, Switzerland
M. De Wild, University of Basel, Switzerland
C.H. Galka, University of Heidelberg, Germany
L.H. Gade, University of Heidelberg, Germany
T.A. Jung, University of Basel and Paul Scherrer Institute, Switzerland
H.-J. Güntherodt, University of Basel, Switzerland
Correspondent: Click to Email
Self-assembly of molecules on surfaces directed by different supramolecular interactions has been widely explored. There are striking examples of molecular surface structures, whose formation is driven by metal co-ordination, dipolar coupling or hydrogen bonding. In contrast to these examples, our aim is the formation of covalently linked planar structures by means of polymerization confined in one or two dimensions. The perylene derivative (DPDI) we investigated belongs to a class of compounds which serve as precursors for the production of photovoltaic devices. Recent investigations using differential thermoanalysis and gravimetry demonstrated that bulk DPDI can polymerize releasing ammonia. Inspired by this observation, we tried to exploit the formation of covalent networks on metallic surfaces and to check the feasibility of such an approach for the formation of stable polymer-nanostructures. For this purpose, thin films of DPDI were prepared on Ag(111) and Cu(111) by evaporation in a UHV setup. In a first step, the supramolecular arrangements were analyzed with a home-built STM. A condensed phase with a rectangular unit cell was found on both substrates if the coverage was in the range of 1ML. After annealing to 580K, a rearrangement of the DPDI molecules into a rhombic unit cell structure was observed. This symmetry change was accompanied by the appearance of a link between individual perylene groups which we identify as covalent bonds. Further evidence, in favor of a covalent bond formation is provided by the shortening of the intermolecular distance of the ad-molecular patterns after the thermal activation. We identify these structures as arrays of 1D polymer rows. For lower coverage in the range of 0.3ML only a mobile phase was detected before annealing. However, upon annealing to 580K a stable 2D network with a honeycomb-like structure was observed which conveniently matches the angles and distances expected for the chemically feasible polymer structure.