A Combined Scanning Tunneling Microscopy and Electrochemical Study of Nickel Electrodeposition on β-Brass

The electrodeposition of Ni on β-brass from Watt's bath was studied by using electrochemical techniques, scanning tunneling microscopy (STM) imaging, and X-ray diffraction. As the electrodeposition current density j was increased from 0.01 to 0.25 A cm-2, both the Ni crystal size (d) and the root mean square roughness of the deposit (ξ) decreased. For j > 0.25 A cm-2 the deposit became rougher due to the growth of large Ni crystals over a background of small Ni crystals. This change in the growth mode appears as a transition in the value of ξ which is promoted by strongly adsorbed intermediates involved in the discharge of Ni2+ ions. The analysis of the dynamic and static roughening exponents resulting from the application of the dynamic scaling theory to the STM images of Ni deposits indicates that the growth of Ni at high current density, i.e. far from the thermodynamic equilibrium, can be described as an aggregation process with a significant contribution of Ni atom surface diffusion.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada