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 x 10(-3) M Ag2SO4 + 10(-2) M H2SO4 + 0.5 M Na2SO4, 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.