In situ FTIR monitoring of Ag and Au electrodeposition on glassy carbon and silicon

Formation of Ag, Au and Ag-Au alloys on Si and Glassy Carbon (GC) electrodes from alkaline cyanide electrolytes was investigated using a combination of electrochemical and spectroscopic techniques. Metal deposition and dissolution processes could be studied in situ by monitoring the v(CN) bands of the metal complexes and the, free cyanide ion in the region between 2000 and 2200 cm(-1) using FTIR reflectance spectroscopy. Under the experimental conditions, two different silver complexes, namely [Ag(CN)(2)](-) and [Ag(CN)(3)](2-) (whilst only one gold complex, namely [Au(CN)(2)](-)), were identified. In the case of the Ag-Au alloys, both species co-deposit even in the activation region, where Ag reduction is expected to be the main reaction. Experimental results indicate that in a mixed electrolyte containing equal amounts of Ag and Au, Ag deposition is thermodynamically favoured ( E-eq(0), (Ag)>E-eq(0), (Au)), while Au deposition is kinetically favoured. The Ag-Au alloy deposition follows a progressive nucleation mechanism even at relatively high negative potentials. The morphology and adhesion of all deposits, as well as the alloy composition, were found to be strongly dependent on the deposition conditions. A better adhesion of the films with a higher Au content was observed, due to the formation of a more stable Au-Si bond. (C) 2002 Elsevier Science Ltd. All rights reserved.