A comparative investigation of replication techniques used for the study of (S+Au) sensitized AgBr microcrystals

A full understanding of the chemical sensitization of silver halide microcrystals with nanoscale silver/gold-sulfide clusters requires knowledge of both their nature and distribution on the microcrystal surface. Because direct electron microscopy studies of sensitized silver halide microcrystals are almost impossible, due to the electron-induced release of photolytic silver, one must resort to reliable preparation techniques such as carbon replication or gelatin encapsulation. In the present study different replication techniques are investigated and compared. For cubic and octahedral silver bromide microcrystals, the carbon replica technique in combination with the complexing agent 1,2,4-triazolium-thiolate is favored, because the traditional complexing agent, sodium thiosulfate, itself creates silver sulfide clusters as artifacts, which hampers the investigation of genuine silver-sulfur sensitization centers. Gelatin encapsulation, an alternative to carbon replication, shows severe reduction problems created during the hardening process of the gelatin. Tabular crystals, on the other hand, can be replicated by the latter process without the need for hardening.