NONLINEAR-OPTICAL SPECTROSCOPY OF THE AG(111) SURFACE IN AN ELECTROLYTE AND IN VACUUM

In this paper, we investigate the electronic structure of a metal surface in the presence of aqueous electrolyte and an applied potential by optical second harmonic generation (SHG). We have obtained the detailed wavelength dependence (lambda(SH) = 300-350 nm) of the SH response from Ag(111) in both an aqueous electrolyte and in ultrahigh vacuum (UHV) and find that, when the Ag (111) electrode is biased at the potential of zero charge (PZC), the SH response can be strongly correlated with the SH response in UHV. For the surface in both environments, there is a sharp peak near 3.82 eV. Possible contributing factors to this peak are discussed. In the electrochemical environment, the effect of applied potential on the SH response at longer wavelengths (nonresonant regime) is consistent both with previous observations at fixed frequencies and predictions of the surface charge density (SCD) model. At resonant wavelengths, there is a dramatic deviation from behavior predicted by the SCD model, a result consistent with previous experiments at discrete wavelengths.