Photographic Sensitization of the AgBr(100) Surface and the Effect of Au and S in Latent Image Formation: A Detailed Theoretical Mechanism
✍ Scribed by Abds-Sami Malik; John T. Blair; William A. Bernett; Francis J. DiSalvo; Roald Hoffmann
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 390 KB
- Volume
- 146
- Category
- Article
- ISSN
- 0022-4596
No coin nor oath required. For personal study only.
✦ Synopsis
Recent experimental characterization of the Au-doped reconstructed AgBr(111) surface has been used to construct a theoretical model (using an approximate molecular orbital method) of that surface. The surface consists of a half-layer covering of Ag segregated into rows 7.07 A s apart, with the Au in interstitial sites just below the surface. Our calculations indicate that the surface Ag s-orbital form states at the bottom of the conduction band, which could serve as trapping sites for photoelectrons. The gold atoms do not contribute directly to these states. We also construct models (based on experimental data) of the AgBr(100) surface with ledge and kink type point defects and of an AgBr(111) : Ag 2 S(100) interface. The theoretical models provide a mechanism for the formation of a latent subimage through trapping of photoelectrons and subsequent pairwise distortion of the surface Ag. This model predicts that latent subimage formation is more favorable on AgBr(111) surfaces than on AgBr(100) surfaces and that Au contributes to the stability of a latent subimage cluster. Calculations of an AgBr(111) : Ag 2 S(100) interface show that interface formation leads to a smaller band-gap. The formation of a latent subimage cluster is thus facilitated.
1999 Academic Press
Silver halides have been the basis of photography for over 150 years. In modern photographic "lm, the light sensitive surface consists of an emulsion of AgBr (which has the NaCl structure type) microcrystals of octahedral and tabular (presenting the (111) surface) or cubic (presenting the (100) surface) morphologies. The former is found in most commercial preparations and is empirically known to possess greater photographic sensitivity than the latter (1). Gold and sulfur dopants are also added to further improve photographic sensitivity (1). Experimental evidence shows that silver sul"de, silver gold sul"de, and Au are formed during Former a$liation.
To whom correspondence should be addressed.
They, in fact, emerge carrying not much charge in our calculations. The ionicity is greater toward the surface than in the bulk. Please see Ref. (5) for details.
516