BRANCHED FRACTAL PATTERNS IN NONEQUILIBRIUM ELECTROCHEMICAL DEPOSITION FROM OSCILLATORY NUCLEATION AND GROWTH

The branched fractal structures formed by non-equilibrium electrodepos ition of metals' have for several years been considered as model syste ms for the study of branching and fractal growth processes generally(2 -6). Most studies have focused on the large-scale structure of the dep osits, but the question of how the branching pattern emerges from the nucleation and growth of the polycrystalline metal at the microscopic scale remains unclear. Here I present experimental and theoretical res ults which suggest that branched electrodeposits may arise from an osc illatory character in the nucleation kinetics. For this kind of deposi tion, nucleation is probabilistic but biased towards higher electric f ields. I suggest that a given nucleation event is followed by a recove ry phase before a subsequent event is possible. This oscillatory natur e generates a polycrystalline deposit, the grain size of which determi nes the level of 'noise' which is amplified by the familiar laplacian ('fingering') instabilities of non-equilibrium growth(2-6) into a macr oscopically fractal structure.