Molecular self-assembly: Quantifying the balance between intermolecular attraction and repulsion from distance and length distributions

Molecular self-assembly on surfaces constitutes a powerful method for creating tailor-made surface structures with dedicated functionalities. Varying the intermolecular interactions allows for tuning the resulting molecular structures in a rational fashion. So far, however, the discussion on the involved intermolecular interactions is often limited to attractive forces only. In real systems, the intermolecular interaction can be composed of both attractive and repulsive forces. Adjusting the balance between these interactions provides a promising strategy for extending the structural variety of molecular self-assembly on surfaces. However, this strategy relies on a method to quantify the involved interactions. Here, we investigate a molecular model system of 3-hydroxybenzoic acid (3-HBA) molecules on calcite (10.4) in a ultrahigh vacuum. This system offers both anisotropic short-range attraction and long-range repulsive dipolar interactions between molecules, resulting in the self-assembly of molecular stripes. We analyze the stripe-to-stripe distance distribution and the stripe length distribution and compare these distributions with analytical expressions from an anisotropic Ising model with additional repulsive interactions. We show that this approach allows the extraction of quantitative information about the strength of the attractive and repulsive interactions. Our work demonstrates how the detailed analysis of the self-assembled structures can be used to obtain quantitative insight into the molecule-molecule interactions.