Smoothening Mechanism of Thiourea on Silver Electrodeposition. Real Time Imaging of the Growth Front Evolution

Ag electrodeposits were grown on a polycrystalline Ag cathode at either 0.01 or 1 mA cm - 2 from aqueous 5 × 10 - 3 M Ag 2 SO 4 + 10 - 2 M H 2 SO 4 + 0.5 M Na 2 SO 4, in the absence and presence of different amounts of thiourea (TU). The cathode/solution interface evolution in a quasi-bidimensional electrochemical cell was followed with a video microscope imaging system. From TU-free solution a nodular morphology at 0.01 mA cm - 2 and a branched morphology at 1 mA cm - 2 were observed. At 0.01 mA cm - 2 the presence of TU drove the interface motion to a stable roughness regime by suppressing the nucleation and growth of instabilities. Accordingly, the characteristics of the growth front were consistent with the predictions of the Edwards−Wilkinson equation for the interface motion. At 1 mA cm - 2, those electrodeposits grown in the presence of TU showed a decrease in both the nucleation and growth rates of instabilities, although they were not fully suppressed.