Surface Diffusion of Azabenzene s-Triazine Molecules on a Strong Interacting Graphene–Metal System

Abstract

We report on an ultrahigh vacuum study of the surface diffusion and growth of the azabenzene 1,3,5-triazine molecule on epitaxial graphene on Rh(111) at low temperature by means of scanning tunneling microscopy. It reveals the arrangement of well-ordered molecules in a hexagonal lattice of 6.3 Å periodicity, giving rise to irregularly shaped islands. Although the substrate is considered to be a strongly interacting graphene–metal system, the graphene layer still decouples the individual molecules from the metal underneath, allowing more than one preferential configuration of the molecule arrangement on the surface. This fact is revealed from our nucleation study, which shows important parameters such as the critical nucleus equal to one, meaning that already a dimer would be stable at the surface, and the energy needed for a single molecule to diffuse (Ed = 80 ± 9 meV). This energy is only slightly higher by some meV than those obtained on other much less interacting graphene-like systems as highly oriented pyrolitic graphite (HOPG) and graphene on Pt(111). This shows that even for a strong interacting graphene–metal interface, azabenzene molecules as s-triazine, are physisorbed allowing easy self-organization even at temperatures as low as 40 K.