SFG study of thiocyanate ion adsorption onto polycrystalline Au electrode and electrodeposited metallic thin films

The sum frequency generation (SFG) characteristics of thiocyanate ions adsorbed on polycrystalline gold electrodes and on electrodeposited cobalt and nickel films are presented. The aim of this study is to compare the ion adsorption behavior on these metals by studying the CN stretching mode variations. In the cobalt-containing solution, a transition in the band frequency potential dependence between the naked gold surface and the cobalt-covered one has been evidence for potentials more positive than the one required for bulk cobalt deposition, suggesting that an anion-induced underpotential deposition process is taking place. The change of the SFG spectrum shape, the higher slope value of the band potential dependence, and the lower band frequency value observed on the bulk electrodeposited Co and Ni films suggest differences in the interaction strength, related to the d band filling of the substrate, and in the adsorption geometry of thiocyanate ions on these metals compared to the gold surface.