The present study highlights the changes in morphology in a Sn matrix during pulsed electrodeposition of a Sn−Cu near-eutectic alloy with varying current density in an acidic electrolyte. 3D image construction has been employed using SHAPE V7.3; Shape Software: Kingsport, Tennessee, USA to replicate the shape of grown crystals and analyze the results. It is observed that the growth morphology changes with the introduction of high index planes at higher current densities. Furthermore, a growth pattern occurs with high index planes formed from a stepped structure in low index planes. There has been a change in growth direction from ⟨001⟩ to ⟨110⟩ at higher current densities. At very high current densities, sympathetic or secondary nucleation is observed.
Copper has been electrodeposited on copper (FCC) and mild steel (BCC) substrates from acidic sulphate bath with and without cetyl trimethyl ammonium bromide at 0.25, 2, 6 and 9 V. It is found that the surface morphology varies with the change in overpotential, but not with the change in substrate. On the contrary, the crystal shape is found to be independent of the applied overpotential, but varies with the bath chemistry or choice of substrate.
In this paper, we discuss the effect of potential difference and current density on the crystal morphologies of copper electrodeposits. Their individual roles have been identified by creating a passivation layer in situ at the anode during deposition, which instantaneously reduces the current density in the system while maintaining a high potential difference. It is observed that the crystal shape is decided by the potential difference and current density determines the rate at which that shape is achieved. In a copper system, at high overpotentials, coherent twin boundaries are formed due to their low formation energy as compared to high angle grain boundaries, high index surface planes, etc. Without the presence of any foreign species like H 2 bubbles during the crystallization process, the slowest growth direction is identified to be <1 1 1>. The passivation layer is formed due to a pH distribution in the electrolyte caused by the high electric field. A new methodology to explain the formation of the passivation layer is proposed, which is performed by analyzing the current transients generated using Kirchhoff's Laws.
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