Micro-fabricate a device as shown here
, consisting of a gold line (say 200 nm wide and 40 nm thick) and a silver line (same dimensions) which is perperndicular to the gold line. One of the ends of the silver line is ~300 nm from the middle of the gold line (so that they make an incomplete “T”). Cover the junction area with Ag2S. Wire both Au and Ag lines and stick the whole thing in SEM (we have a tool which allows us to do it). Apply a bias to switch the contact ON and observe the picture in the SEM.
The intention is to see a dendritic “tree” of silver atoms growing from the silver electrode to the gold one. Also dissolving it at reverse bias would be kinda cool.