Intermolecular Repulsion in Molecular Self-Assembly on Bulk Insulator Surfaces

• Applicant: Professorin Dr. Angelika Kühnle
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391648454

In this project, we aim for exploring long-range repulsive interactions for controlling molecular self-assembly of organic molecules on bulk insulator surfaces. While short-range attractions are widely used to steer molecular structure formation on surfaces in a rational fashion, intermolecular repulsion has so far not been considered in a systematic way. Only few examples exist in literature demonstrating long-range intermolecular interaction in molecular self-assembly on surfaces. For most of these examples, interaction of electrical dipoles has been suggested as the origin of the repulsion. A systematic investigation of the general nature of this repulsion is, however, still lacking. From the prospective of steering structure formation, the rational use of intermolecular repulsion in molecular self-assembly bears the potential to enlarge the parameter space available for controlling the resulting structures´ shape and distribution on the surface.To develop strategies for making use of repulsive interactions in molecular structure formation on surfaces in a rational fashion, we will address three questions by performing scanning force microscopy measurements carried out in ultra-high vacuum at variable temperatures.First, we will investigate to what extend intermolecular repulsion is a general driving force in molecular self-assembly on surfaces. Clearly, even if a certain repulsion is present, experimental conditions might hamper the manifestation of the repulsion in the resulting molecular structures.Second, while repulsion of electrical dipoles appears as a very reasonable origin for intermolecular repulsion, the experimental confirmation for this assignment is still largely missing. To this end, temperature and coverage-dependent experiments are needed that shed light on the details of the interaction potential.Finally, we want to make use of the balance between short-range attraction and long-range repulsion for steering the resulting structures´ shape and distribution on the surface. To this end, we will systematically vary the involved interactions by changing functional groups at the molecule and by changing the substrate. Besides the interactions´ strengths and ranges, a key aspect here is to consider the effect of directionality, i.e., the spatial anisotropy of the involved interactions. We will compare our experimental results with Monte Carlo simulations to validate that a certain interaction characteristics will result in the experimentally observed structural motifs.Including intermolecular repulsion in the description of molecular self-assembly will allow for enhancing the structural variety that can be obtained in molecular structure formation on surfaces in a rational fashion.

• DFG Programme: Research Grants
• International Connection: United Kingdom
• Co-Investigator: Dr. Ralf Bechstein
• Cooperation Partner: Dr. Andrea Floris