Order beyond a monolayer: The story of two self-assembled 4,4′-bipyridine layers on the Sb(111) | ionic liquid interface

Abstract

In this study, it has been shown that the ordering of organic molecules is not limited to a highly organised self-assembled monolayer on the electrode's surface. At the interface between semi-metallic Sb(111) electrode and ionic liquid with 4,4′-bipyridine addition, two distinctive stacked adsorbed layers upon each other have been identified by applying in situ scanning tunnelling microscopy and electrochemical impedance spectroscopy methods. The first adlayer in contact with the electrode consists of tightly packed ordered rows. The second adlayer, on top of the first, is characterised by low surface concentration, and its unit cell was obtained experimentally. In addition to experimental data, the likely distribution of 4,4′-bipyridine molecules in the first adlayer has been described using density functional theory calculations combined with machine learning. The gained insights of organic's adsorption from ionic liquids are of fundamental and practical importance in the development of nanoelectronic devices.