Photographic Sensitization of the AgBr(100) Surface and the Effect of Au and S in Latent Image Formation: A Detailed Theoretical Mechanism

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 ? 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):Ag2S(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):Ag2S(100) interface show that interface formation leads to a smaller band-gap. The formation of a latent subimage cluster is thus facilitated.