Tuning intermolecular interaction in long-range-ordered submonolayer organic films

The future success of organic electronic devices strongly depends on the ability to tailor the properties of thin films and interfaces. This calls for well-ordered thin films. However, their properties are dominantly influenced by the formation of the first molecular layer representing a template for further growth. The development of the first layer—in turn—depends on the fine balance of molecule–substrate and molecule–molecule interaction. The latter is usually attractive owing to van der Waals forces and causes the formation of islands and small crystalline grains. Here, we report on organic adsorbates exhibiting a repulsive intermolecular interaction. With increasing coverage, Sn-phthalocyanine molecules continuously rearrange on Ag(111) in a series of ordered superstructures. They always fill the surface terraces homogeneously and maximize the domain size. Thicker films also exhibit extremely large, monocrystalline grains and potentially enable bulk-like properties for thin films. The intermolecular interaction can be tuned by cooling and becomes attractive below ∼120 K. The force between molecules deposited on a surface during the growth of an organic film is usually attractive. But for certain metal phthalocyanine molecules, this force can change with temperature from attractive to repulsive, resulting in unusual ordering behaviour.