Formation and Properties of Sub-Image and Latent-Image Silver Specks. Part I: Thermodynamics of Silver Speck Formation

The formation of latent image specks has been discussed so far as a sequence of steps (Ag1,→Ag2 -→Ag3-→ .) which allegedly leads from precursors (Ag1, Ag2,...) finally to full image centres. This reaction scheme demands that a continuous growth of silver specks by electron capture regardless of the size of the specks takes place as the result of exposure. Sub-image specks obtained by a weak pre-exposure, or reduction sensitization specks are believed to be such precursors of latent image. If silver speck formation is treated as a process of phase formation, calculations suggest that such a continuous growth does not take place: Very small specks (e.g.Ag1, Ag2,) tend to capture holes and are thus destroyed by exposure. Growth by electron capture requires a minimum size of the silver specks which depends on the value of the exposure-induced supersaturation in the crystal.