Morphological Transitions from Dendrites to Nanowires in the Electroless Deposition of Silver

A morphological transition from dendrites to nanowires in the electroless deposition of silver by galvanic displacement of copper seeds is investigated as a function of seed size. The transition to dendritic growth is interpreted as arising from local reaction anisotropies interacting with the global solute concentration distribution. Reactions were performed on substrates bearing lithographically patterned grids of copper posts with sizes ranging from 1 to 50 pm. When copper seed size exceeds 10 pm, the deposition reaction consumes silver cations at a sufficient rate to create ripple-like Mullins-Sekerka instabilities in their distribution. The resulting concave growth fronts produce branched, dendritic structures. For copper posts smaller than 3.5 mu m, cation consumption is balanced by diffusion and the growth front's advance toward the bulk, leading to networks of nanowires formed as the local reaction anisotropy favors growth by stacking along Ag(111) planes.