XPS investigations on the interactions of 1,6-hexanedithiol/Au(1 1 1) layers with metallic and ionic silver species

Surfaces of densely packed aliphatic (di)thiol/gold self-assembled monolayers (SAMs) with one thiolate–gold bond per molecule are prepared and used as models for functionalized polymer/metal interfaces. In detail, the penetration of metallic or ionic silver species through 1-hexanethiol/Au(1 1 1) and 1,6-hexanedithiol/Au(1 1 1) layers is investigated with X-ray photoelectron spectroscopy (XPS). These organic films are readily penetrated by silver species as well during Ag vapor deposition as during immersion in silver sulfate solution. As a driving force for the layer penetration strong Ag–thiolate interactions are discussed. Experimental proof for such bonding is provided by several findings. Ag–thiolate bond fission is observed to occur at higher temperatures than Au–thiolate decomposition. Furthermore, the deposition of metallic silver via UHV evaporation reveals the formation of Ag–thiolates at the SAM surface in the case of 1,6-hexanedithiol/Au(1 1 1) SAMs. Finally, the characterization of the dithiol/gold system indicates the chemisorption of hydrated Ag+ ions at the interface between the SAM and a silver sulfate electrolyte.