Electrodeposition of Ag-Ni films from thiourea complexing solutions

Ag-Ni alloy films were electrodeposited from thiourea-based acidic solutions. Electrochemical studies confirmed the strong polarization of Ag deposition due to the strong complexation of Ag+ with thiourea, bringing the onset of Ag and Ni deposition closer, potentially favoring alloy formation. The as-deposited films were very fine grained (less than 20 nm) and consisted of various phases: a supersaturated solid solution of Ni in Ag and a Ni-rich nanocrystalline or amorphous phase, preferentially formed at grain boundaries. Ag-rich films were smooth, while a higher Ni content resulted in increasingly rough and porous films. Decomposition of the metastable phase and precipitation of the pure elemental phases occurred upon thermal annealing at 600 °C. Reduction of thiourea induced by Ni deposition led to sulfur incorporation in the films, up to 20 at.%.