True perylene epitaxy on Ag(110) driven by site recognition effect

We present a STM study of room temperature perylene adsorption on the Ag(110) surface. We have found a 2D perylene crystalline phase coexisting with the perylene liquid phase under thermal equilibrium. The reversible precipitation of the liquid phase at sub-monolayer coverage reveals the well ordered chiral crystalline phase existing in two enantiomorphic configurations of the ((-2)(3) (5)(2)) and ((2)(3) (5)(-2)) symmetry. This chiral phase is spatially separated into the 2D enantiopure islands of tens of nanometers size randomly distributed on the substrate and surrounded by the liquid medium. Analysis of surface registry of the crystalline phase combined with modeling of the intermolecular interactions indicates that its structure and symmetry is determined by a specific balance between the intermolecular attraction and intrinsic ability of the perylene aromatic board to recognize adsorption sites. The recognition effect was found to be strong enough to pin half of the perylene molecules into defined adsorption sites providing the structure skeleton. The attractive intermolecular interaction was found to be strong enough to bind another half of the molecules to the perylene skeleton shaping the true epitaxial structure.