Theory of second-harmonic generation at the metal-electrolyte interface

A model for second-harmonic (SH) generation at the metal-electrolyte interface is proposed and treated by means of an electronic density-functional calculation. The dependence of the SH signal on the electrode charge is studied for different values of system parameters which represent different aspects of the metal-medium interaction. Characteristic differences between the SH signal at a free metal surface and for the same metal in contact with electrolyte are predicted in the range of negative surface charges and near the zero charge point. At large positive charges (when the surface electronic profile is almost entirely hidden within the metal positive ionic background) the solvent effect is small and the dependence of the SH signal approaches the corresponding curve for the free metal surface. General trends in the signal dependence upon ionic adsorption are established.