Interface metal/silver halide

The gold treatment undoubtedly results in a replacement of at least some latent image silver by gold. It is possible, as already mentioned, that the nuclei have been increased in size by a physical development effect, but this seems unlikely for the short times involved. The maximum effect is obtained within 5 minutes under the experimental conditions used. Accordingly, it appears that the increased rate of development is the result of the changed properties of the metal/silver halide interface, which now involves metallic gold instead of silver. 

Ag3CuIg]4 clusters, in which copper(I) is three coordinated, whereas silver(I) is four coordinated or both three and four coordinated, respectively, from the metal iodides and tetraphenylphosphonium iodide in acetonitrile solution, may also be seen as lending support to the hypothesis that the primary process at the solution-crystal interface is cation-halide packing, the naked metal ion diffusing into the appropriate interstices. 

In contrast, in most ion-selective membranes the charge conduction is done by ions. Thus, a mismatch between the charge-transfer carriers can exist at the noble metal/membrane interface. This is particularly true for polymer-based membranes, which are invariably ionic conductors. On the other hand, solid-state membranes that exhibit mixed ionic and electronic conductivity such as chalcogenide glasses, perovskites, and silver halides and conducting polymers (Lewenstam and Hulanicky, 1990) form good contact with noble metals. 

Until about 1960 the metal-electrolyte interface was probably the most extensively investigated surface. Semiconductor electrodes also have a considerable history, dating back at least as far as Bequerel s work on silver halides/ Almost all the early studies with semiconducting electrodes were performed with materials of uncontrolled and generally unknown properties. 

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