ANISOTROPIC NONLINEAR OPTICAL-RESPONSE FROM SILVER ELECTRODES DURING THIN-FILM DEPOSITION

Rotational anisotropy in the optical second harmonic generation from Ag(111) and Ag(110) single-crystal electrodes is used to measure relative changes in the components of the nonlinear susceptibility of the interface during charging and adsorption processes. The application of a dc field and underpotential deposition of lead and thallium are studied. Some common features are noted for thallium adsorption on the two crystal faces, and the results are compared to a similar study on Cu(111). The isotropic components show changes in both magnitude and phase that continue up to the formation of the first monolayer. The anisotropic tensor elements in both cases are relatively insensitive to the formation of the first adlayer. The magnitude of these anisotropic terms is enhanced upon the formation of the second adatom layer. The results are analyzed with a model that assumes a Langmuir adsorption isotherm and stepwise deposition. Probable mechanisms for the enhanced signals and reasons for the adsorption behavior are proposed. © 1990 American Chemical Society.