AVS 53rd International Symposium
    Surface Science Wednesday Sessions
       Session SS2+EM-WeA

Paper SS2+EM-WeA8
One-Dimensional Supramolecular Assemblies on Stepped Surfaces: What Makes Them Extend into the Mesoscale Length Regime?

Wednesday, November 15, 2006, 4:20 pm, Room 2004

Session: Organic Film Growth and Characterization
Presenter: J. Schnadt, University of Aarhus, Denmark
Authors: J. Schnadt, University of Aarhus, Denmark
E. Rauls, University of Aarhus, Denmark
Wei Xu, University of Aarhus, Denmark
J. Knudsen, University of Aarhus, Denmark
R.T. Vang, University of Aarhus, Denmark
B. Hammer, University of Aarhus, Denmark
F. Besenbacher, University of Aarhus, Denmark
Correspondent: Click to Email
On perfect single crystal surfaces small organic molecules can self-assemble to form ordered one- and two-dimensional networks based on hydrogen bonding and other non-covalent interactions (see, e.g., Ref. 1). Such networks can grow very large and extend into the meso- and macroscale length regimes. Most real surfaces of interest, however, are afflicted with defects such as monatomic steps. These defects typically hinder the formation of large-scale networks. We show here for a particular example that it is possible to overcome this obstacle by choosing the right combination of surface and organic molecule. In the present case we investigated the self-assembly of 2,6-naphthalene-dicarboxylic acid (NDCA) on a stepped Ag(110) surface and compared it to the self-assembly of the same molecule on the Ag(111) and Cu(110) surfaces. The STM and XPS results show that NDCA on Ag(110) forms macroscopic-scale one-dimensional and directional structures across the step edges with maximum lengths in the micrometer range, notwithstanding the stepped character of the surface. This stands in contrast to the other surfaces, where the step-crossing behaviour is not observed. The experimental results together with density functional theory calculations show that the primary driving force for the formation of these long one-dimensional assemblies is hydrogen bonding, and that these bonds form also at the Ag(110) step edges. The bond formation across the step edges is driven by a combination of different factors, including the strength and bond directionality of the hydrogen bonds, the assembly directionality mediated by the substrate, and a sufficient flexibility of the adsorbate molecular backbone. A subtle balance of these factors, which depends on the particular adsorbate and the particular substrate, is required to achieve the observed step-edge tolerance of the assembly. @FootnoteText@ @footnote 1@ J. V. Barth, G. Costantini, and K. Kern, Nature 437, 671 (2005).