Optical properties of silver thin films: Three-parameter spectroscopic ellipsometry studies

Silver thin films were prepared by an rf-magnetron sputtering technique. Real-time spectroscopic ellipsometry was employed to investigate the initial growth behavior of the silver films, and the optical properties of the films were determined by a three-parameter ellipsometric technique. In the initial growth stages, the films showed anomalous absorption in the visible wavelength region, which moved to longer wavelength as the film grew. This anomaly was related to the size oi the metal clusters and to the interaction between them. In other words, a strong dipole oscillation of electrons occurred from one side of the cluster to the other, and the interaction between the clusters increased as the film grew. A giant dipole model with a Lorentz oscillator was adopted to account for the optical properties of grain-like metal thin films. We also observed a decrease of reflectance in the cluster films around 3.8 eV, which is a characteristic of bulk silver. However, the d-band transitions were absent in the thin films, indicating a lack of translational symmetry in these films.