Self-Assembly of Cobalt-Phthalocyanine Molecules on Epitaxial Graphene on Ir(111)

We have studied the adsorption and self-assembly of cobalt phthalocyanine (CoPc) on epitaxial graphene grown on iridium (111) by scanning tunneling microscopy (STM), Auger electron spectroscopy, and low-energy electron diffraction (LEED). CoPc deposited on graphene/Ir(111) at room-temperature self-assembles into large, well-ordered domains with a nearly square unit cell. On the basis of the observed LEED pattern and STM images, a detailed structure for the overlayer is proposed. Despite the corrugation of the moire pattern of graphene on Ir(111), its hexagonal symmetry is not translated to the CoPc layer. This is in contrast to systems with stronger graphene-metal interaction that makes graphene on Ir(111) a convenient, clean, and well-defined model system for studying molecular doping of graphene.