Long-Range Order Induced by Intrinsic Repulsion on an Insulating Substrate

Abstract

An ordered arrangement of molecular stripes with equidistant appearance is formed upon the adsorption of 3-hydroxybenzoic acid onto calcite (10.4) held at room temperature. In a detailed analysis of the next-neighbor stripe distances measured in noncontact atomic force microscopy images at various molecular coverages, we compare the observed stripe arrangement with a random arrangement of noninteracting stripes. The experimentally obtained distance distribution deviates substantially from what is expected for a random distribution of noninteracting stripes, providing direct evidence for the existence of a repulsive interaction between the stripes. At low molecular coverage, where the average stripe distance is as large as 16 nm, the stripes are significantly ordered, demonstrating the long-range nature of the involved repulsive interaction. The experimental results can be modeled with a potential having a 1/d(2) distance dependence, indicating that the observed long-range repulsion mechanism originates from electrostatic repulsion of adsorption-induced dipoles solely. This effect is particularly pronounced when local charges remain unscreened on the surface, which is characteristic of nonmetallic substrates. Consequently, the observed generic repulsion mechanism is expected to play a dominant role in molecular self-assembly on electrically insulating substrates.