The role of adatoms in the surface enhanced Raman scattering has been examined. The potential dependence of the SERS intensity of pyridine and $Ag^0-Cl^-$ was investigated, and the current response to the potential was also checked simultaneously. We have confirmed that there is a 'switching point' and irreversible loss of intensity during the potential sweep. These results are convincing evidences that the adatoms cause a crucial effect on the SERS.
Much weaker intensity of SERS of pyridine in a nonaqueous electrochemical system compared with that in the aqueous case is also explained by using the adatom model.
