Selective Cooperative Self-Assembly between an Organic Semiconductor and Native Adatoms on Cu(110)

Abstract

We investigate molecular adsorption, film growth, and selfassembly for titanyl phthalocyanine (TiOPc) on Cu(110) in ultrahigh vacuum using low-temperature scanning tunneling microscopy (LT-STM). Three unique molecular adsorption configurations are identified, two of which are referred to as "O-down" and one as "O-up", each differing in the molecular registry with the surface. Even though disorder dominates film growth to coverages in excess of 1 monolayer in the native thin film, extended self-assembled 1D configuration-dependent nanoribbons form upon annealing of the film. The STM data reveal that the nanoribbons consist of "O-down" TiOPc and a Cu skeleton, anchoring cooperatively on the Cu(110) terraces. Agent-based simulations show that nanoribbons grow and elongate due to anisotropic adatom attachment rates along the two major surface directions. The study reveals the importance of molecule− adatom interactions for novel approaches toward nanostructuring organic semiconductor/metal interfaces.

Configuration-specific electronic structure of strongly interacting interfaces: TiOPc on Cu(110)

“…A dramatic thermally driven surface coarsening was demonstrated for several members of the Pc family on Cu(110) [41], and we showed previously that for TiOPc, this involves a configuration-selective process of cooperative self-assembly between Cu adatoms and "O-down" molecules ( Fig. 4) [36]. Insight from this configurationspecific process is key to understanding the electronic structure transformation that accompanies surface texturing.…”

“…3(b)] shows amorphous film growth for a surface coverage near 1 ML, which is corroborated in angle-resolved UPS by the fact that all molecular features are nondispersive [40]. Interspersed in the amorphous film are small aggregates of primarily "O-down" molecules (regions of bright contrast on the terrace) which are decorating small islands of Cu adatoms [36].…”

“…2). As detailed in prior work, the species with a central feature of bright contrast is assigned to the configuration with the oxygen atom directed toward the surface ("O-down") [36]. This assignment is supported by asymmetry in the molecule, in terms of both interlobe distances and apparent lobe heights, which reflect a tilted molecular geometry on the surface.…”

“…This assignment is supported by asymmetry in the molecule, in terms of both interlobe distances and apparent lobe heights, which reflect a tilted molecular geometry on the surface. Conversely, the fourfold symmetric species with no central feature reflects a flat adsorption geometry on the surface and is assigned to the "O-up" configuration [36]. The two configurations have different dipole orientations and orbital overlap with the surface, and are thus subject to unique configuration-dependent interfacial interactions.…”

“…The two configurations have different dipole orientations and orbital overlap with the surface, and are thus subject to unique configuration-dependent interfacial interactions. For example, dispersive interactions with the ligand favor adsorption coplanar with the surface and at terrace sites for "O-up" adsorbates [ Fig the molecule and the step edge play a more prominent role in "O-down" adsorbates and lead to preferential adsorption at these sites [36]. .…”