title: Self-assembly of strongly dipolar molecules on metal surfaces.
abstract: The role of dipole-dipole interactions in the self-assembly of dipolar organic molecules on surfaces is investigated. As a model system, strongly dipolar model molecules, p-benzoquinonemonoimine zwitterions (ZI) of type C6H2(⋯ NHR)2(⋯ O)2 on crystalline coinage metal surfaces were investigated with scanning tunneling microscopy and first principles calculations. Depending on the substrate, the molecules assemble into small clusters, nano gratings, and stripes, as well as in two-dimensional islands. The alignment of the molecular dipoles in those assemblies only rarely assumes the lowest electrostatic energy configuration. Based on calculations of the electrostatic energy for various experimentally observed molecular arrangements and under consideration of computed dipole moments of adsorbed molecules, the electrostatic energy minimization is ruled out as the driving force in the self-assembly. The structures observed are mainly the result of a competition between chemical interactions and substrate effects. The substrate's role in the self-assembly is to (i) reduce and realign the molecular dipole through charge donation and back donation involving both the molecular HOMO and LUMO, (ii) dictate the epitaxial orientation of the adsorbates, specifically so on Cu(111), and (iii) inhibit attractive forces between neighboring chains in the system ZI/Cu(111), which results in regularly spaced molecular gratings.
authors.affiliation: Department of Physics, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
authors.forename: Donna A
authors.initials: DA
authors.lastname: Kunkel
authors.affiliation: Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, 30-060 Krakow, Poland.
authors.forename: James
authors.initials: J
authors.lastname: Hooper
authors.affiliation: Department of Chemistry, 331 Natural Sciences Complex, Buffalo, New York 14260, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Simpson
authors.affiliation: Department of Chemistry, 331 Natural Sciences Complex, Buffalo, New York 14260, USA.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Miller
authors.affiliation: Lab de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 67081 Strasbourg, France.
authors.forename: Lucie
authors.initials: L
authors.lastname: Routaboul
authors.affiliation: Lab de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 67081 Strasbourg, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Braunstein
authors.affiliation: Institut de Physique et Chimie des Mateŕiaux de Strasbourg (IPCMS UMR 7504 CNRS) and Lab of Nanostructures in Interactions with their Environment (NIE), Université de Strasbourg, 23 Rue du Loess, 67034 Strasbourg, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Doudin
authors.affiliation: Department of Physics, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
authors.forename: Sumit
authors.initials: S
authors.lastname: Beniwal
authors.affiliation: Department of Physics, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Dowben
authors.affiliation: Department of Physics, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
authors.forename: Ralph
authors.initials: R
authors.lastname: Skomski
authors.affiliation: Department of Chemistry, 331 Natural Sciences Complex, Buffalo, New York 14260, USA.
authors.forename: Eva
authors.initials: E
authors.lastname: Zurek
authors.affiliation: Department of Physics, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
authors.forename: Axel
authors.initials: A
authors.lastname: Enders