Self-Assembled n-Alkanethiolate Monolayers on Underpotentially Deposited Adlayers of Silver and Copper on Gold

Abstract

This paper describes the use of gold films that contain underpotentially deposited (upd) metal layers of copper or silver as substrates in the generation of self-assembled monolayers (SAMs). The assembly of alkanethiols to form SAMs is compatible with the presence of the upd layer and forms a system that contains an interlayer of the upd metal that is between the gold substrate and the adsorbed organic monolayer. The assembly on these substrates can accommodate both polar and nonpolar tail groups, and the resulting SAMs span the range of wettabilities (θa(H2O) = <15° to 113°). The SAMs on the upd substrates have highly organized structures that are distinct from those that form on the parent bulk metal surfaces. In addition, the upd metal has a more noble redox potential than the corresponding bulk metal and allows an expanded potential window in cyclic voltammetry. For example, ferrocene-terminated alkanethiolsdespite having redox potentials that are positive of bulk silvercan be assembled onto silver upd substrates and form stable electroactive SAMs. The presence of the upd layer improves the stability of alkanethiolate monolayers against both desorption at elevated temperatures and molecular exchange within thiol-containing solutions.