Latent-image generation by deposition of monodisperse silver clusters

Silver cluster ions (Ag₁{}⁺$, ${Ag}₃⁺, Ag₄{}⁺$, ${Ag}₅⁺, Ag₇{}⁺$, and ${Ag}₉⁺) generated in a sputtering arrangement were filtered in energy selected by size, and deposited onto specimens containing binder-free AgBr microcrystals prepared from a photographic emulsion. Development was observed after exposure to beams containing Ag₄{}⁺$ or larger aggregates. No development occurred after exposure to beams of smaller cluster sizes. These experiments prove directly the existence of a ``critical'' size required for catalyzing development. This size may depend on the development conditions (e.g., the redox potential), as suggested by theories.