Abstract:

 Electrochemical oxidation reduction cycle (ORC) is the most common way to create SERS activity at silver electrode surfaces. In the present study, two different types of ORC procedures, a special ORC and a normal ORC, have been used. The reduction potential of the special ORC was about -1.3V, negative to the potential of zero charge (PZC), while for the normal ORC, that was around -0.3 V, positive to the PZC. The SERS activity created by the special ORC was stable at the potentials negative to the PZC and that created by the special ORC was stable at the potentials negative to the PZC and that created by the normal ORC was stable at the potentials positive to the PZC. Using STM and SERS, it was found that the highly actives SERS sites were metastable and liable to decompose as the applied potential approach to the PZC due to the rearrangement of the surface atoms (clusters). To avoid the decomposition, a high concentration of Cl- was used so that the SERS active sites could be stabilized as the potential passed across the PNC and the SERS spectra of water at the potential negative or positive to the PZC were able to be obtained under this condition. Therefore, SERS activity can be extended to much wider region. A comparison of the SERS behavior created by the two types of ORC is discussed in detail.

Key words: Surface enhanced Raman scattering, Oxidation reduction cycle(ORC), Adsorption, Surface active sites, Scanning tunneling microscopy, Silver electrode