The Concentration Process in the Formation of Development Centres in Silver Halide Microcrystals*

Abstract

AbstractThis paper discusses the processes whereby silver atoms are concentrated at a few sites during exposure to form development centres in silver halide emulsion grains. Two models are used. With lhe first model, lhe chemically sensitized grain has small surface monolayer islands of AgsS molecules with Ag2 molecules adsorbed al vacant sites around their edges. Exposure results in the photu-oxidation of these Ag2 molecules with liberation of conduction electrons and charge-compensating interstitial silvcr ions. There are many shallow traps in the grains with depths less 1han 5 kT al room temperature which do not altract and trap electrons. If the electron were trapped, the free energy would be increased by the trapping process on account of the enormous density of stales in the conduction band. An effective trap or concentration speck with a depth greater than 16 kT is first formed during exposure by the c(llnbination of an interstitial silver ion and an electron at an Ag2 molecule. followed by lhe ads...