Role of step edges on the structure formation of α-6T on Ag(441)

Abstract

Controlling the orientation of organic molecules on surfaces is important in order to tune the physical properties of the organic thin films and, thereby, increase the performance of organic thin film devices. Here, we present a scanning tunneling microscopy (STM) and photoelectron emission microscopy (PEEM) study of the deposition of the organic dye pigment α-sexithiophene (α-6T) on the vicinal Ag(441) surface. In the presence of the steps on the Ag(441) surface, the α-6T molecules exclusively align parallel to the step edges oriented along the [11¯0]-direction of the substrate. The STM results further reveal that the adsorption of the α-6T molecules is accompanied by various restructuring of the substrate surface: Initially, the molecules prefer the Ag(551) building blocks of the Ag(441) surface. The Ag(551) termination of the terraces is then changed to a predominately Ag(331) one upon completion of the first α-6T monolayer. When closing the two layer thick wetting layer, the original ratio of Ag(331) and Ag(551) building blocks ( ≈ 1:1) is recovered, but a phase separation into microfacets, which are composed either of Ag(331) or of Ag(551) building blocks, is found.