A detailed theoretical mechanism for photographic sensitization of AgBr surfaces: Construction of inorganic/organic composite materials with W(6)S(8) clusters and ditopic ligands

Empirical evidence suggests that AgBr microcrystals presenting the (111) surface have greater photographic sensitivity than those presenting the (100) surface. It is also known that Au and S impurities enhance latent image formation and thus confer greated photographic sensitivity to AgBr. Recent experimental data revealing the structure of the reconstructed AgBr(111) surface, and identifying the Au impurity sites, have been used to construct a theoretical model (within the framework of extended Huckel theory) of the reconstructed AgBr(111) surface with and without Au impurities. The reconstructed surface consists of a half-layer covering of Ag ions segregated into rows 7.07 A apart. The calculations indicate that these surface Ag rows give rise to states at the bottom of the conduction band, which could serve as shallow trapping sites for photoelectrons. The theoretical model provides a mechanism for the formation of a latent image cluster through trapping of photoelectrons in the low lying state and subsequent pairwise distortion of the surface Ag within the rows to form Ag-Ag bonds. In these calculations, the Au impurity enhances latent image formation by a partial reduction of the surface Ag through electron transfer to the low lying state, thus requiring fewer photoelectrons to complete the reduction of surface Ag. A model of the (100) surface with ledge and kink defects shows that pairwise distortions at these defects are not as energetically favorable. A model of the AgBr/Ag;A theoretical model of the hypothetical compound...