title: Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces.
abstract: We investigated the adsorption of 4-methoxy-4'-(3-sulfonatopropyl)stilbazolium (MSPS) on different ionic (001) crystal surfaces by means of noncontact atomic force microscopy. MSPS is a zwitterionic molecule with a strong electric dipole moment. When deposited onto the substrates at room temperature, MSPS diffuses to step edges and defect sites and forms disordered assemblies of molecules. Subsequent annealing induces two different processes: First, at high coverage, the molecules assemble into a well-organized quadratic lattice, which is perfectly aligned with the <110> directions of the substrate surface (i.e., rows of equal charges) and which produces a Moiré pattern due to coincidences with the substrate lattice constant. Second, at low coverage, we observe step edges decorated with MSPS molecules that run along the <110> direction. These polar steps most probably minimize the surface energy as they counterbalance the molecular dipole by presenting oppositely charged ions on the rearranged step edge.
authors.affiliation: Aix-Marseille Univ, IM2NP, Faculté des Sciences de St. Jérome, F-13397 Marseille France; CNRS, IM2NP, Faculté des Sciences de St. Jérome, F-13397 Marseille France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Nony
authors.forename: Franck
authors.initials: F
authors.lastname: Bocquet
authors.forename: Franck
authors.initials: F
authors.lastname: Para
authors.forename: Frédéric
authors.initials: F
authors.lastname: Chérioux
authors.forename: Eric
authors.initials: E
authors.lastname: Duverger
authors.forename: Frank
authors.initials: F
authors.lastname: Palmino
authors.forename: Vincent
authors.initials: V
authors.lastname: Luzet
authors.forename: Christian
authors.initials: C
authors.lastname: Loppacher