Spectroscopic multiple angle reflection and transmission ellipsometry of aggregated gold films

Aggregated gold films exhibit anisotropic optical properties, showing a well-known plasma resonance absorption in the particles in the visible region when incident light with an electric field parallel to the film plane is used. Little is however known about the optical properties of the film in the direction perpendicular to its surface. By using the technique of spectroscopic multiple angle reflection and transmission (SMART) ellipsometry developed in our laboratory, it was possible to determine the three components of the anisotropic effective optical constants of the aggregated gold films. Samples of different thicknesses have been prepared and their optical properties determined in the visible and near infrared spectral regions. The experimental values of the anisotropic optical constants were then compared to those given by an effective medium theory taking into account mirror-image effects in the substrate. Satisfactory agreement between theory and experiment has been found.