Determining optical properties of thin films by modified attenuated total reflection with a charge coupled device

Abstract

Thin films of silver produced by vacuum deposition deteriorate and tarnish when exposed to the atmosphere. This aging is due to the gradual buildup of a layer of Ag2S. When the silver layer is the plasma in an attenuated total reflection (ATR) configured waveguide the buildup of this extra layer can be observed as a shift in the angle of the resonance‐type reflection minimum. Here a modified ATR configuration which utilizes a charge coupled device has been used for accurate measurement of the angle shift of the resonance minimum. Comparison of theoretical with experimental results for angle change leads to a value for thickness buildup of the Ag2S layer. Results are also given for the change in the refractive index with time of a MgF2 overcoat as atmospheric water is adsorbed into its columnar microstructure. This paper describes a simple, qualitative way for determining refractive index change in a freshly deposited thin film.