EIS combined with SERS:: a tool to study the adsorption of S2O32- and PMT in silver electroplating conditions

The adsorption behaviour of S2O32- and 1-phenyl-5-mercaptotetrazole (PMT) is part of the complex silver electroplating process, and is studied in this work by combining ac impedance measurements, determining the capacitive behaviour of the silver-electrolyte interface, and Surface Enhanced Raman Spectroscopy, allowing the quantitative detection and identification of adsorbed species. S2O32- strongly interacts with the silver surface in the potential region from -100 to -300 mV, and causes a strong increase of the double-layer capacity with respect to that measured in the S2O32- free supporting electrolyte. At more negative potentials, a weak physisorption of S2O32- at silver drastically lowers this effect. The adsorption of PMT causes a strong decrease of the double-layer capacity which is the reverse from the observed behaviour for S2O32-. Also, no effect of the applied potential is observed here. When representative deposition solutions with S2O32- and PMT together are considered, it is demonstrated that the adsorption behaviour of S2O32- and its effect on the double-layer capacity is hardly affected by the presence of PMT. The adsorption of PMT, on the other hand, is only possible when chemisorbed S2O32- is removed from the surface, i.e., at more negative potentials than -300 mV. (C) 1999 Elsevier Science Ltd. All rights reserved.