Formation, Properties and Stability of Latent Image as a Metal Cluster

Abstract

Silver halides are photo semiconductors, the photo electrons of which react with mobile interstitial silver ions. Without the presence of such a silver cluster, which is called the latent image speck, the crystal will be reduced only after a very much longer time. The number of photons required for latent image speck formation is reduced greatly and may approach the optimum value of four, when at the surface of the micro crystal so-called sensitivity canters have been deposited. While silver speck formation in an undoped AgBr crystal proceeds roughly at random and may occur at any site of the surface as well as in the interior (where it is absolutely useless for development), exposure of a crystal containing sensitivity centers leads to latent image formation exclusively at the site of these centers. This increases greatly the economy of silver formation. An increase of photographic sensitivity is also obtained, when the crystal is doped with very small silver clusters of a size—say, Ag 2 —which is still insufficient to induce development.