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 similar to 120 K.