PUB - Publikationen an der Universität Bielefeld

As part of surface science research, the behaviour and interaction of molecules on a surface and the resulting system’s properties are investigated. The properties depend, among other things, on the structure formed by the adsorbed molecules. The molecules can self-assemble, driven by attractive and repulsive intermolecular interactions and interactions between the molecules and the surface. The research on molecular self-assembly aims to understand and control these interactions and the self-assembly process to create structures with customised properties. While attractive interactions are already part of intensive research in molecular self-assembly, this thesis focuses on the role of repulsive interactions and their quantification. For this, the model system of 3-hydroxybenzoic acid on the calcite(104) surface is investigated with atomic force microscopy in an ultrahigh vacuum at different temperatures and degrees of surface coverage. The adsorbed 3-hydroxybenzoic acid molecules self-assemble into one-dimensional islands (stripes). The islands’ spatial information is extracted from the atomic force microscopy images to get stripe-to-stripe distances and stripe lengths. The distance and length distributions are statistically evaluated and analysed with an analytical model to determine and quantify the interactions dictating the structure. The analysis with the analytical model reveals a coverage-dependent repulsive interaction. The attractive interaction is not clearly coverage-dependent. These observations can be explained by a change in the molecule-surface interaction and the related adsorption-induced dipole moment, causing and primarily impacting the repulsive interaction. The temperature-dependent analysis reveals the length distribution undergoing a complex transformation during equilibration. The shape of the distribution changes several times and reacts sensitively to temperature changes, which is why it constitutes an indicator of the equilibration process’s status. Combined with kinetic observations, the distribution’s shape indicates that the temperature window, where the system is thermodynamically equilibrated after a reasonable waiting time and without desorption, is between 290 to 310 K only. This underlines the importance of temperature and the complexity of its impact on molecular self-assembly. Overall, this work demonstrates that self-assembled structures’ size and distance distributions can be used to obtain qualitative and quantitative insights into kinetic processes and intermolecular interactions in molecular self-assembly.