Optical properties of ultra-thin silver films deposited by thermal evaporation and its application in optical filters

The ultra-thin silver films with different thickness are deposited by resistance thermal evaporation at room temperature, and the optical constants n and k are obtained by using variable angle spectroscopic ellipsometer (VASE) in the spectral range 380-1600 nm. The thickness range of ultra-thin silver film is 5.3-24.9 nm. SEM images on the surface morphology of ultra-thin silver films show that the ultrathin silver films have discontinuous island structure. The volume fraction of solid silver materials in ultra-thin silver films are simulated by Brugeman approximation theory. Dielectric-metal-dielectric (D-M-D) sandwich structure ZnS/Ag/ZnS optical filter is designed with the optical constant of the modified ultra-thin silver films. The average transmittance of the fabricated D-M-D optical filter is as high as 88.5% and peak transmittance is above 90.5% in the wavelength range between 400 and 700 nm. The maximum reflectance was 94.0% in the region of 2000-12000 nm.