Adsorption, interaction, and manipulation of dibutyl sulfide on Cu{111}

This paper describes a low-temperature scanning tunneling microscopy (STM) study of a simple thioether, dibutyl sulfide, on a Cu{111} surface. The literature is full of data about thiol-based monolayers; however, relatively little is known about thioether self-assembly. Thioethers are more resilient to oxidation than thiols and offer the potential for control over nanoscale assembly in two dimensions parallel to the surface. Therefore, robust assembly schemes derived from thioethers may offer a new class of self-assembled systems with novel and useful properties. At a medium surface coverage and a temperature of 78 K, dibutyl sulfide grows in small, highly ordered islands in which the ordering is driven by both the molecule-surface dative bonds and intermolecular van der Waals bonding. Annealing to around 120 K allows diffusion and reordering of the molecules and the formation of large, very well ordered domains with little or no defects. We show high-resolution images of the molecular arrays and propose a model for their packing structure. These data suggest the potential use of thioethers for a variety of self-assembly applications that require control over molecular spacing parallel to the surface. We also show how the STM tip can be used to manipulate individual molecules within the ordered structures and that the arrays can act as a nanoscale abacus. The range of motion of the manipulated molecules inside a regular array reflects the potential imposed upon them by their neighbors.