Optical Properties of Aggregated Silver Films

Abstract

For interpreting the optical properties of aggregated metal films, a modification of Schopper’s model is proposed, based on the assumption that an aggregated film consists of particles in the shape of rotational ellipsoids. Instead of the distribution of the depolarizing factor f in gaussian fashion, which is assumed in Schopper’s model, the logarithmic normal distribution of the axial ratio γ of the ellipsoidal particles was assumed and the parameter σ (standard deviation of the distribution function) was introduced. Besides, the contributions of the dipole interaction between particles and the size-dependent optical constants of the particles were taken into account. Using this modified model, the observed values of silver films continuously measured by ellipsometry during deposition were analyzed and the two parameters, the mean axial ratio γ¯ and the standard deviation σ, were obtained as functions of film thickness. The results showed that as film grows, both γ¯ and σ increase monotonically. Good coincidence of the observed and the calculated absorption spectra from our model seems to show the validity of our modification.