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Volume: 42 | Article ID: art00005
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On the Role of Sulfide Molecules in Photographic Sensitivity
  DOI :  10.2352/J.ImagingSci.Technol.1998.42.3.art00005  Published OnlineMay 1998
Abstract

Models and mechanisms which have been proposed for silver sulfide and silver-gold sulfide sensitization are reviewed. These sulfides are not involved in the primary photochemical processes of the direct photolysis theories of Sheppard, Gurney and Mott, Hamilton, Kanzaki and Tadakuma, and Tani. In these theories, photoelectrons and positive holes are created in pairs and the role of sulfide sensitization in trapping photoelectrons is emphasized. With a chemically sensitized silver halide emulsion grain, there are, however, a large number of equivalent sites at which electron trapping can occur and the theories provide no process for the efficient formation of a development center by the separation of a small number of silver and gold atoms at one particular site. According to the photoaggregation theory, chemical sensitization results in the formation of small monolayer islands of Ag2S and (Ag,Au)S molecules at surface sites with Ag2 molecules adsorbed around their edges. These sensitizing molecules are dissociated by the annihilation of energy quanta with creation of photoelectrons and release of Ago+ or Auo+ interstitial ions. A development center is formed at an Ag2 latent image growth nucleus precursor by two effective events. In the first event, a photoelectron and interstitial ion combine with an Ag2 molecule to form a Ag3 or AuAg2 molecule that adsorbs a Ag+ ion to give an Ag4+ or AuAg3+ latent image growth nucleus. In the second event, this positively charged nucleus attracts and traps a photoelectron and the positive charge is restored by the effective adsorption of an Ago+ ion giving an Ag5+ or AuAg4+ development center of minimum size, adsorbed to a sulfide monolayer island. This center grows by the repetition of these electronic and ionic events and this provides an efficient concentration process.

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J. W. Mitchell, "On the Role of Sulfide Molecules in Photographic Sensitivityin Journal of Imaging Science and Technology,  1998,  pp 215 - 221,  https://doi.org/10.2352/J.ImagingSci.Technol.1998.42.3.art00005

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