Effect of underpotential deposition on the surface enhanced Raman effect

The first experimental observation of surface enhanced Raman scattering (SERS) from benzotriazole (BTA) on Ag as a function of the underpotential deposition of Tl is reported. The complete quenching of SERS before completion of the submonolayer deposition of Tl is attributed primarily to displacement of BTA from the Ag surface. The decrease in intensity of SERS is found to be approximately linear with the number of Tl ions deposited. But the rate of quenching of SERS is dependent on the initial surface topography. Increased electron scattering is proposed as an additional quenching mechanism. Upon Tl deposition, frequency shifts for one of the BTA lines are determined to be three times larger than that expected based on a surface charging mechanism. Mechanisms for SERS based on electronic interactions of the adsorbate and substrate are indicated