Coverage‐Dependent Self‐Assembly of Rubrene Molecules on Noble Metal Surfaces Observed by Scanning Tunneling Microscopy

Abstract

Coverage-dependent self-assembly of rubrene molecules on different noble metal surfaces, Au(111) and Au(100), Ag(111) and Ag(100), is presented. On Au(111), the homochiral supramolecular assemblies evolve with increasing rubrene coverage from very small structures composed of a few molecules, to honeycomb islets, and to one-dimensional chains of supramolecular pentamers. At higher coverage, the racemic mixture of molecules forms close-packed islands. On Au(100), chains of pentamers and two different types of densely packed islands are formed. On the Ag surfaces, exclusively close-packed islands are created, independently of the rubrene coverage. Moreover, the role of the chiral nature of the molecules in the self-assembly process is discussed, as well as the existence of different molecular conformers depending on the supramolecular assembled phase. The observed differences and similarities reflect the influence of the electronic properties and the geometric structure of the various substrates on molecular self-assembly.

Charge Reorganization Energy and Small Polaron Binding Energy of Rubrene Thin Films by Ultraviolet Photoelectron Spectroscopy

“…[22] However, recently, (sub)monolayers of rubrene on Au (111) are reported to formdepending on the specific preparation conditions-manifold supramolecular structures of essentially flat lying molecules as evidenced by scanning tunneling microscopy (STM). [23][24][25][26] Con sequently, the mutual supramolecular stabilization might lead to a conformational transition on a shorter length scale or even to the concomitant occurrence of rubrene in a twisted and a planar conformation in the monolayer on Au (111) or other inert substrates like graphite. In a recent STM study of rubrene on Bi (001) such a coexistence was actually experimentally shown for monolayer coverage.…”

C60 chain phases on ZnPc/Ag(111) surfaces: Supramolecular organization driven by competing interactions

“…31 As a function of coverage, pentamers of rubrene were found to organize into a diffuse network of extended chains, in some cases coincident with the underlying Au(111) herringbone reconstruction. Higher coverage yielded the formation of close-packed islands.…”

“…Organization into network structures, rings or "bubbles," and stripe phases has been observed via scanning tunneling microscopy (STM) in numerous single and multicomponent molecular mixtures. [21][22][23][24][25][26][27][28][29][30][31][32][33] Self-organization can be engineered by controlling specific directional bonding motifs of the molecular components to guide assembly. [26][27][28][29][30] Self-assembly into complex molecular patterns can also be induced, as described above, by competing intermolecular interactions.…”

“…[26][27][28][29][30] Self-assembly into complex molecular patterns can also be induced, as described above, by competing intermolecular interactions. [31][32][33] The molecular architecture in organic layers is typically subject to several weak interactions, such as van der Waals, hydrogen bonding, and electrostatic interactions, that operate on very different length scales. Van der Waals and hydrogen bonding interactions act predominantly on nearneighbors while electrostatic interactions influence structure over many lattice sites.…”

Transient Monolayer Structure of Rubrene on Graphite: Impact on Hole–Phonon Coupling

“…In a 3 previous study of monolayer rubrene on HOPG we showed that the main vibrational energy (determined in a single mode analysis of the vibrational fine structure of the UPS HOMO-derived peak) of the twisted conformation is slightly larger than that of the planar conformation 26 . The thin film structure and the conformation of rubrene on various substrates depend critically on the film thickness 37,[43][44][45] . Thus, in order to cover a thickness regime which is more relevant for device application, we explore the hole-phonon coupling beyond monolayer coverage in our combined angle-resolved UPS and metastable atom electron spectroscopy (MAES) study of vacuum-sublimed rubrene on HOPG Experimental section Rubrene (two times purified in high-vacuum) thin films were prepared by vacuum sublimation on clean HOPG surfaces using resistively heated quartz crucibles with deposition rates of about 0.25 Å/min as controlled by a quartz crystal microbalance.…”