Combined roughness and electric polarization for the local-field enhancement of the second harmonic response from a silver-electrolyte interface

A nanoscale rough silver film is electrodeposited from a silver cyanide aqueous solution and its growth is monitored by second harmonic generation (SHG). For growth by potential step into the diffusion controlled region, a maximum in the SHG intensity is always obtained for an equivalent silver film thickness of ∼60 nm, based on the charge consumed. The SH intensity decreases for thicker but smoother films. A study as a function of an applied static electric field for an already grown film shows that the combination of nanoscale roughness and electric polarization is able to yield large enhancement of SH signal intensities. From a microscopic analysis of the data, it is shown that the nonlinear surface current perpendicular to the interface exhibits a nonlinear dependence with the applied potential, owing to the combination of roughness and electric polarization.