The Structural Characteristics of Certain Silver Films

Abstract

The structural characteristics of three types of silver films which have found general use as photocathode bases in television image analyzers and similar electronic devices are discussed. They are classified as mosaics and translucent films. Two types of mosaics are discussed, (1) the reduced oxide dust film, and (2) the agglomerated sputtered or evaporated film. A characteristic of the first is a wide range in particle size (<1−30μ in films photographed), those below 3 microns being greatest in number. A critical temperature, approx. 600°C, is observed in reduction of the oxide films above which there is a distinct liquid phase in the silver‐silver oxide system resulting in a radical change in the final film structure. The process of agglomeration is traced from the continuous through the mosaic state in the second type film. The characteristics are a smaller and more uniform particle size than the reduced oxide type. Particle size and spacing is readily controlled and reproduced. The range in initial thickness of films investigated is approximately 0.01−0.2 microns. The third type or translucent film is a composite consisting of a silver mosaic superposed on an electrically conducting film of relatively high light transmission. Platinum is chosen as the most suitable metal for this subfilm and is protected from destructive forces such as oxidation and alloying with the silver mosaic by an intermediate film of silica or aluminum oxide.