Évolution de certaines propriétés optiques des lames métalliques très minces

Abstract
In order to obtain consistent results in the study of optical properties of thin films, it is essential that the films should be prepared and studied in as perfect a vacuum as possible. It is further necessary that the surface of the targets on which the films are deposited should be of a chemically simple and perfectly defined nature. An apparatus permitting this study has been constructed at the Faculty of Science of Marseille; it has thus been possible to prepare thin films and to study the variations of their optical properties. The first results obtained with silver films, of thickness under 10 μ, and deposited on glass by thermal evaporation, have shown that these films undergo, immediately after their preparation, two important changes. The first corresponds to a " spontaneous ageing " of the films in the vacuum; the second one is produced by the action of the gas to which the surface of the films are exposed. When the phenomenon of the spontaneous ageing appears to be completed, one can produce a "reversibility effect " which shows itself in variations of the reflection factors if the films are placed alternately in a vacuum and in air. A systematic study of the changes of the optical properties of targets and films of chemically welldefined nature is in progress.