The Penetrability of a Thin Metallic Film Inside the RF Field

Thin metallic film was widely applied in various areas. Especially, recently we are planning to apply it in a “Secondary emission enhanced photo-injector”, in which a diamond cathode is coated with a metallic film on its back to serve as a current path. The thickness of the film is originally considered to be in the order of 10 nm, which is much less than the skin depth, by a factor of almost 200. One would think intuitively that the RF filed would penetrate such a thin film. However, we found it is not true. The film will block most of the field. This paper addresses theoretical analysis as well as the experimental results, and demonstrates that the penetrability of a thin film is very poor. Consequently, most of the RF current will flow on the thin film causing a serious heating problem.