OPTICAL ANISOTROPIES OF AG SINGLE-CRYSTALS

We present a model for the electromagnetic response of Ag single-cryst al surfaces that accounts for both interband and intraband transitions , taking advantage of the localized nature of the dipole moments assoc iated with the transitions from the d levels. The response functions d isplay structure near the plasma frequency which are related to the re sonant dipolar oscillations localized near the first crystalline plane . The surface response is incorporated in a calculation of the optical reflectance which yields large corrections to Fresnel's formulae, of the order of 10%. Furthermore, these corrections depend on the surface orientation and on the angle between the polarization vector and the surface principal directions. We have confirmed this result experiment ally for the (110) face of Ag. We have performed reflectance differenc e spectroscopy (i.e. normal incidence ellipsometry) on this face, and measured the real and imaginary parts of the anisotropy in the reflect ion amplitude for incident polarization along the [11OBAR] and [001] d irections. Measurements have been carried out on freshly polished and clean samples as well as on oxidized samples. We compare these results with the calculated anisotropies derived from the model.