Thin Ag/Bi coatings as epsilon-near-zero material with low optical losses

Abstract

The work presents a study of the influence of the deposition conditions and the composition on the optical and structural properties of thin Ag/Bi coatings. Two methods for thin films deposition were used for this purpose: co-evaporation of silver and bismuth and deposition of multilayer coatings by alternating very thin layers of both metals. The results from the X-ray analyses showed that both methods allow the realization of thin Ag–Bi layers with controlled composition. The complex permittivity, ε = ε’+i.ε” of the thin films was determined by spectral ellipsometry. A significant reduction in the values of ε” was observed at a bismuth content of 20–50 at. % in the thin Ag–Bi films, while the ε′ values stay negative and vary between 0 and -1 in a wide spectral range 0.6–3.5 eV. The analysis of the dielectric loss function, Im{-1/ε} showed that the silver-bismuth interface influences significantly the properties of Ag–Bi thin films.