A COMBINED SCANNING-TUNNELING-MICROSCOPY AND ELECTROCHEMICAL STUDY OFNICKEL ELECTRODEPOSITION ON BETA-BRASS

The electrodeposition of Ni on beta-brass from Watt's bath was studied by using electrochemical techniques, scanning tunneling microscopy (S TM) imaging, and X-ray diffraction. As the electrodeposition current d ensity 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 (xi) decre ased. For j > 0.25 A cm(-2) the deposit became rougher due to the grow th of large Ni crystals over a background of small Ni crystals. This c hange in the growth mode appears as a transition in the value of xi wh ich is promoted by strongly adsorbed intermediates involved in the dis charge of Ni2+ ions. The analysis of the dynamic and static roughening exponents resulting from the application of the dynamic scaling theor y 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 contributio n of Ni atom surface diffusion.