There are a number of beliefs about black and white instant photography that possibly started with the very earliest Polaroid prints, done before the process was well understood, and refined. One such misconception is that the positive image is formed of metallic silver. Since DTR is one of the earliest important commercial forms of nanotechnology and self-assembly, I recommend

PHOTOGRAPHIC SILVER HALIDE DIFFUSION PROCESSES – ANDRE ROTT, EDITH WEYDE - FOCAL PRESS

For basic information about image formation in DTR mode. It is interesting that Edith Weyde actually first appears to have invented the process leading to instant photography.

In the nanotech world, silver DTR is a hot topic today.