As one of the important mechanisms of SERS, the charge transfer (CT) ehnancment requires the strong interfaction of the adsorbed species with the substrate in order to permit the transition of charge between the metal Fermi level (energy state) and the molecular orbital~(1). The high enhancement needs the match of the energy gap between the Fermi level (or surface state) and the orbital energy level of the adsorbed molcules with the energy of the incident light. The electrode Fermi level is usually adjusted by the applied potential to satiosfy the CT resonance. For the electrochemical reaction pr0cess, the froniter orbital energy level of the reacting surface species should be greatly different for the adsorbed molecules. Thus, it is interesting to test the additional SERS enhancement induced by electrochemical reaction.
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