Surface-enhanced Raman scattering on uniform platinum-group overlayers: preparation by redox replacement of underpotential-deposited metals on gold.

The preparation of Pt-group metal films on roughened gold electrodes by utilizing spontaneous redox replacement of an underpotential-deposited (upd) copper or lead monolayer with a Pt-group metal cation solute is described. The resulting films display intense surface-enhanced Raman scattering (SERS) for adsorbates bound to the overlayer and free from substrate interferences. This strategy provides a useful alternative, at least for platinum, to the constant-current electrodeposition method commonly utilized to prepare SERS-active Pt-group metal films (Zou, S.; Weaver, M. J. Anal. Chem. 1988, 70. 2387). Similarly to related earlier studies, the film uniformity (specifically, the absence or otherwise of residual Au “pinhole” sites) was tested by employing carbon monoxide, and also ethylene, as “probe” chemisorbates, since they yield vibrational frequencies on Au that are blue-shifted from the corresponding bands for adsorbate bound to Pt-group metal sites. While a single redox replacement of upd Cu with Pt(...