Optical second harmonic generation spectroscopy from Ag(001) using s-polarized excitation

The s- and p-polarized second harmonic generation (SHG) from Ag(001) under electrochemical control was measured as a function of the sample orientation about its surface normal. Our experiments were performed over a range of second harmonic photon energies surrounding the onset of interband transitions, and for different values of the applied potential on either side of the potential of zero charge. We used only s-polarized incident light to eliminate most of the susceptibilities that usually contribute to SHG, leaving two bulk-derived contributions (ζ, which depends upon the crystal orientation, and γ, which is insensitive to crystal orientation), and one surface susceptibility (χzxx). Our results suggest that, of these, χzxx is less significant, with ζ being considerably larger than γ. Both of these show little spectral variation. Even more surprising is the result that γ demonstrates a sensitivity to changes in the applied potential. This could be associated with changes in the characteristics of electron scattering by the surface barrier, which would indirectly influence the dynamics of electrons in the bulk.