The potential dependence of Surface Enhanced Raman Scattering (SERS) intensity during Oxidation-Reduction Cycle (ORC) was studied in various electrochemical environments. Adatomic effect on SERS was confirmed from the characteristic variation of SERS intensities of pyridine, $Cl^-$ and continuum background from Ag and Cu electrodes during ORC. SERS was also affected by other resonance effects such as charge transfer and Surface Plasmon (SP) excitation as well as the number density of surface adsorbed molecules. SERS intensities and the observed frequencies of vibrational modes were changed slightly with incident wavelength, the species of metal and the electrochemical surface condition of electrodes.
We have first observed above 40℃ the irreversible loss of SERS intensity from the Cu electrode in electrochemical system. Judging from the irreversible variation of SERS intensity and the reflectivity of Cu electrode surface near -1.45Vsce in nonfaradaic region, it is confirmed that there is significant adatomic effect on the reflectivity of the electrode surface as well as on SERS.
Cu adatoms are also diffused away to the surface defects at higher temperature than Ag adatoms in electrochemical environment as in Ultra High Vacuum(UHV) environment. Especially the result that Cu adatoms diffuse away at temperatures elevated by 60K~70K in electrochemical environment than in UHV environment suggests that the mobility of adatom is decreased in solution by the formation of a surface complex with probe molecules, water molecules and other ions.
Though Cu adatoms can stabilize Ag adatoms on the surface of Ag electrode at room temperature, they can not stabilize above 40℃ in electrochemical system, i.e Cu adatoms on the surface of Ag electrode have the same binding energy as on the surface of Cu electrode. Ag adatoms are considered to be diffused away to the surface defects along a channel approximately defined by the local minima of the potential energy surface.