XPS investigations on the interactions of 1,6-hexanedithiol/Au(111) 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 photoclectron 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 inter-face between the SAM and a silver sulfate electrolyte. (C) 2002 Elsevier Science B.V. All rights reserved.