Molecular self-assembly on surfaces is a promising strategy for producing large, atomically ordered structures with desired properties. On the other hand, self-assembled structures can also be used to investigate whether it is intermolecular interactions or interactions with the surface that play a key role in how the molecules arrange on the surface. This has been used to study how the corrosion inhibitor 2-mercaptobenzimidazole behaves on the atomically clean surface of copper with a crystallographic orientation of Cu(111) using scanning tunneling microscopy (STM).
STM is based on tunneling of electrons between an atomically sharp tip and the sample. Since the current is exponentially dependent on the distance, this enables very accurate measurement of the surface corrugation, which, together with the sharp tip, allows us to image topography with atomic resolution. To do so it is important to prepare a clean surface. Alternating cycles of ion sputtering and annealing have been used to prepare clean copper samples. After characterization in STM, molecules were deposited on the sample in ultra high vacuum by thermal evaporation. The evaporation rate was kept approximately while the time the sample was exposed to the molecular beam was varied, which resulted in different concentrations on the surface. Varying the substrate temperature between different experiments limits the energy molecules have to self assemble, which results in different self assembled structures. To elucidate the binding the structure of the resulting layer bases on STM images of the surface had to be determined. Because STM is not directly chemically sensitive density functional theory (DFT) simulations were used to verify the proposed models.
Several self assembled structures suggest that the energy scales of competing interactions must be similar. High mobility even at very low temperatures opposes the idea that strong binding to certain sites on the surface is crucial for corrosion prevention.
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