Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces

Laurent Nony (1) , Franck Bocquet (1) , Franck Para (1) , Frederic Cherioux (2) , Eric Duverger (2) , Frank Palmino (2) , Vincent Luzet (2) , Christian Loppacher (1)

1 IM2NP - Institut des Matériaux, de Microélectronique et des Nanosciences de Provence
2 FEMTO-ST - Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174)

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. 285

Mots clés: organic molecule; noncontact atomic force microscopy; alkali halide surface; self-organization; zwitterion

Domaines: Autre [cond-mat.other]; Acoustique [physics.class-ph]; Matériaux; Micro et nanotechnologies/Microélectronique; Chimie organique

Laurent Nony, Franck Bocquet, Franck Para, Frederic Cherioux, Eric Duverger, et al.. Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces. Beilstein Journal of Nanotechnology, 2012, 3, pp.285-293. ⟨10.3762/bjnano.3.32⟩. ⟨hal-01702352⟩