Self-Assembly of N,N′-Di(n-butyl)-1,3,8,10-tetramethylquinacridone Governed by Metallic Surface Features of a Ag(110) Substrate

We present scanning tunneling microscopy (STM) measurements combined with density functional theory (DFT) calculations to study the relationship between self-assembly characteristics and interaction motifs for organic molecules [here, N,N′-di(n-butyl)-1,3,8,10-tetramethylquinacridone (TMDBQA)] on a Ag(110) surface, which exhibits a distinctive surface, featuring regions, such as atomically flat terraces and steps. It was found that Ag atoms on the surface terraces are weaker in chemical reactivity than those on the step edges, which leads to the different molecule–substrate interactions and thereby, the different self-assembly structures. The carbonyl oxygen on TMDBQA forms strong coordinative bonds with Ag atoms at the step edge, which is responsible for the formation of adsorbate-induced facets, and directs the arrangement of the molecules with respect to the steps. The DFT calculations demonstrate that with the facet formation, the adsorption energy between the molecule and substrate increases and the intermolecular binding energy decreases. By comparing the hydrogen-bonded self-assembled monolayer of N,N′-di(n-butyl)quinacridone on the Ag(110) surface, we concluded that the formation of adsorbate-induced facets is not favored when molecules bind to each other by strong and directional intermolecular interactions.