Controlling factors for the conversion of trifluoroacetate sols into thin metal fluoride coatings

Metal fluoride films were prepared from trifluoroacetate sols by a spin-coating method. Effects of preparation conditions on the deposition of fluoride films have been examined in order to control the thickness and the refractive index of the films. It was suggested that the fluoride was formed by the thermal decomposition of the trifluoroacetate sols generating gaseous phases such as (CF₃CO)₂O, CO and CO₂. This reaction mechanism seemed to largely effect the deposition of the fluoride films in terms of the formation of pores. Characteristics of the fluoride films could be changed by varying the heat treatment. The refractive index of the MgF₂ films decreased with increasing heating temperature, which might result from the increased porosity of the films. Drying the film before the heat treatments was effective in the control of the refractive index.