Intermolecular Repulsion in Molecular Self-Assembly on Bulk Insulator Surfaces
Final Report Abstract
In this project, we wanted to explore the impact of repulsive molecule-molecule interactions during molecular self-assembly on surfaces kept in ultrahigh vacuum. Starting point of the project was the system of 3-hydroxybenzoic acid on calcite (10.4), which was known to exhibit self-assembly into stripes. These stripes do not arrange randomly on the surface, but show a characteristic stripe-to-stripe distance distribution. In order to take this non-random distribution as an indication for repulsive interactions, kinetic effects need to be ruled out. As a first step, we have collected a large amount of data, demonstrating that the measured stripe distance and length distributions remain stable at a given temperature while the molecules possess mobility. To avoid artifacts especially in the length distribution, large-scale images need to be collected with high pixel resolution. The large statistic required for this project prompted us to develop a software routine to analyze large-scale images in an automatic manner. The project focused on three scientific tasks. First, we wanted to explore whether the observed repulsion is limited to 3-hydrobenzoic acid on calcite or constitutes a more general phenomenon. To this end, other molecules have been tested, namely 3-aminobenzoic acid, 3,5-dihydroxybenzoic acid and 4-ethynylbenzoic acid, which all show repulsive effects. So far, however, the class of molecules tested is limited to benzoic acid derivatives and calcite as a substrate. In the second part of the project, we focused on understanding the nature of the intermolecular repulsion. We could confirm that adsorption-induced electric dipoles would fit to the experimentally obtained data. A close collaboration with theory partners resulted in the development of an analytical model which now enable to also study other potentials than dipole-dipole repulsion. In this way, we can now evaluate whether or not the experimental data would also justify other potentials. Moreover, the comparison of experiment and theory now allows for extracting the strength of both the attractive and repulsive interactions from fitting the analytical model to the experimentally obtained distance and length distributions. The limits of the analytical model were tested by comparing the analytical model with Monte Carlo simulations. Finally, we wanted to use the repulsive interaction to steer both the distribution and shape of molecular islands on surfaces. This part of the project was delayed by the lab lock down due to the Corona pandemic.
Publications
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Kinetic control of molecular assembly on surfaces, Commun. Chem. 1 (2018) 66
Chiara Paris, Andrea Floris, Simon Aeschlimann, Julia Neff, Felix Kling, Angelika Kühnle, Lev Kantorovich
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Molecular Self-Assembly: Quantifying the Balance between Intermolecular Attraction and Repulsion from Distance and Length Distributions, J. Phys. Chem. C 124 (2020) 21583
Christoph Schiel, Maximilian Vogtland, Ralf Bechstein, Angelika Kühnle and Philipp Maass
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Molecular Stripe Patterns on Surfaces in the Presence of Long- Range Repulsive Electrostatic Interactions: Monte Carlo Simulations and Mean-Field Theory, J. Phys. Chem. C 125 (2021) 20650
Christoph Schiel, Maximilian Vogtland, Ralf Bechstein, Angelika Kühnle and Philipp Maass
