Dependence of the optical properties of UHV deposited silver thin films on the deposition parameters and their relation to the nanostructure of the films

Abstract

Silver films were deposited on glass substrates under different deposition conditions, i.e. different film thicknesses, deposition rates and deposition angles. Their optical properties were measured by spectrophotometry in the spectral range of 185–3300 nm. The Kramers–Kronig method was used to analyze the reflectivity curves of the silver films to obtain their optical constants. The influence of substrate temperature on the microstructure of thin metallic films, the structure zone model (SZM), is well established, whereas there has been some previous work on the influence of film thickness and morphology, deposition rate and deposition angle on the microstructure and morphology of thin films. An effective medium approximation (EMA) analysis was used to establish the relationship between the atomic force microscopy results, SZM predictions and EMA results, and hence the optical properties of silver thin films. The predictions of the Drude free-electron theory are compared with experimental results for dielectric functions of Ag films produced under different deposition conditions. The real part of the dielectric constant increases with film thickness and decreases with increasing deposition rate and with increasing incidence angle, whereas the imaginary part of the dielectric constant decreases with increasing film thickness and deposition rate and with decreasing incidence angle over the whole energy range measured, including the interaband and interband regions.