Time Dependence of Surface Enhanced Raman Scattering at Silver in the Presence of Underpotentially Deposited Lead and Its Implications for the Roles of Surface Roughness

The recovery of the surface enhanced Raman scattering response for pyridine and Cl^-adsorbed to roughened polycrystalline Ag substrates upon controlled deposition and quantitative stripping of underpotentially deposited Pb is presented. Recovery data are presented for both adsorbate vibrational features as a function of Pb coverage between 0.0 and 1.4 monolayers. The time dependence of the recovery behavior at potentials corresponding to 0.2, 0.5, and 1.0 fractional Pb monolayer is also presented. The onset of SERS irreversibility is correlated with current-time transients for Pb overlayer formation. Loss of SERS recovery after the deposition and stripping of greater than ca. 0.7 fractional Pb monolayer and at times during monolayer deposition is discussed in terms of structural rearrangements of the Pb overlayer which result in an irreversible loss of atomic-scale roughness features.