Disruption of Molecular Ordering over Several Layers near the Au/2,8-Difluoro-5,11-bis(triethylsilylethynyl) Anthradithiophene Interface

The transition from an electrode-dominated ordered monolayer structure to a bulk-like thin film crystal structure of 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT) is observed to occur over at least the first four molecular layers near the electrode surface. Scanning tunneling microscopy studies of the growth of diF-TES-ADT on Au(111) show that the first two molecular layers assemble with aromatic planes parallel to the substrate surface. The monolayer structures are highly stable and well-ordered, while the bilayer structures are more loosely packed and poorly ordered. Subsequent diF-TES-ADT growth results in a more bulk-like layer containing standing up molecular configurations approaching the (001) crystal face as observed by grazing incidence wide angle X-ray scattering measurements. However, the third and fourth monolayers also show poor long-range ordering and an apparent height modulation that indicate significant strain effects from the substrate still persist.