Monitoring Cu nodule formation using Ni marker layers

We have used Ni marker layers to study the evolution of the characteristic spheroidal nodule morphology in electrodeposited Cu films. Ultrathin Ni layers were electrodeposited in-between Cu layers, and cross sections prepared by electrochemical polishing. During growth of a typical spheroidal feature, the edge (i.e. where there is a discontinuity in the surface slope) traces out a straight line in the cross-sectional image. At high overpotential, the cross-sections show nodule-on-nodule growth, giving rise to the well known cauliflower morphology. Rotating disk electrode studies reveal that, surprisingly, the absolute diffusion layer thickness does not appear to play a major role in the development of spheres.

► Ni marker layers to monitor electrodeposited Cu nodule morphological evolution.
► The edges of the nodules trace out a straight line.
► Difference in growth between spheres and hemispheres.
► Nodule on nodule growth at high overpotential.
► No dramatic effect of the diffusion layer thickness on the film morphology.