Electrochemical island growth

The ability to independently dictate the shape and crystal orientation of islands in electrocrystallization remains a significant challenge. The main reason for this is that the complex interplay between the substrate, nucleation, and surface chemistry are not fully understood. Here the kinetics of 3D island growth for copper on ruthenium oxide is studied. The small nucleation overpotential leads to enhanced lateral growth and the formation of hexagonal, disk-shaped islands. The amorphous substrate allows the nuclei to achieve the thermodynamically favorable orientation, i.e. a <111> surface normal. Island growth follows power law kinetics in both lateral and vertical directions. At shorter times, the two growth exponents are equal to 1/2 whereas at longer times lateral growth slows down while vertical growth speeds up. Accordingly, a growth mechanism is proposed, wherein the lateral growth of disk-shaped islands is initiated by attachment of Cu adatoms on the ruthenium oxide surface onto the island periphery while vertical growth is initiated by 2D nucleation on the top terrace and followed by lateral step propagation. These results indicate three criteria for enhanced lateral growth in electrodeposition: (i) a substrate that leads to a small nucleation overpotential, (ii) fast adatom surface diffusion on substrate to promote lateral growth, and (iii) preferential anion adsorption to stabilize the basal plane.;The surface roughness evolution, during isolated island growth, island coalescence, and continuous film growth, has also been studied as a function of island shape and island density. It is shown that the surface width wsat(l,t) initially follows anomalous scaling in the isolated island growth regime but exhibits normal scaling during the early stages of continuous film growth. Furthermore, the short length scale roughness is dependent primarily on island shape while the long length scale roughness is dependent on island density.;Electrochemical deposition of metals onto foreign substrates usually occurs through Volmer-Weber island growth, and hence the structure and properties of thin films are critically dependent on the mechanism of nucleation and growth. For example, high nucleus densities are essential for achieving island coalescence at small thickness. A new approach to control thin film microstructure through control of island geometry is demonstrated. It is shown that by promoting anisotropic island growth, film coalescence can be achieved at smaller thickness and with lower island densities.