Electrode potential dependence of SERS

SER spectra of 0.05 M pyridine in 1M aqueous KC1 recorded as the silver electrode potential was swept through an ORC at 5mV s t. The upper traces (a) show the H20 band, the lower ones (b) show pyridine bands. (Reproduced with permission from ref. 14.) 

Although the foregoing account is greatly simplified in that it takes no account of the vitally important roughness features of the surface, nor of its atomic nature, the presence of defects, the pH of the electrolyte, etc., it nonetheless provides a useful model for understanding the observed potential dependence of SERS effects. 

Since colloidal particles of silver and gold also give large SERS effects, it is useful to consider these as disconnected microelectrodes. Controlled variations in the potential at the interface between silver sol particles and electrolyte solution have been achieved by adding the Eu3+/Eu2+ redox system and varying the concentration ratio [22]. From measurements of SER spectra of pyridine adsorbed on the silver sol, the potential-dependent effects have been found to be identical with those given by bulk silver electrodes. These experiments also demonstrated that the intensity ratio of the pyridine Raman bands at ca. 1010 and 1040 cm-1 may be used as a simple but effective measure of sin-face potential for colloidal metals. 

Pyridine certainly is the most extensively studied compound in the SERS literature. The potential dependence of its vibrational band intensities as a silver electrode is swept through its ORC at a rate of 5mVs-1 is shown [14] in Fig. 13. The intensity of the strongest band reaches a maximum at - 0.9 V (SCE), in keeping with the model described previously in this section and illustrated in Fig. 12. Also consistent with the model is the fact that the SERS-enhanced H20 band at ca. 3500 cm 1 becomes weaker as H20 is displaced from the electrode surface by Py. However, there is no increase in the H20 band intensity when the potential is swept beyond the PZC, as might be expected from the condition illustrated by Fig. 12(E). 

Since it is claimed that SERS effects are displayed by all adsorbates, it would be fruitless to attempt anything approaching a comprehensive review 

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