Heterogeneous nucleation - current transients under chemical reaction control

Abstract

Heterogeneous nucleation on catalytic surfaces plunged into a fluid is described through a stochastic model. To generate this non-equilibrium process we assume that the turn on of a electrostatic potential triggers a complex dynamics that includes a free Brownian motion, a reaction kinetic and a stimulated migration before the final adhesion of ions on the surface (electrode). At, when the potential is switched on, the spatial symmetry is broken and a two-stage process is developed. First the ion undergoes a change in its electrochemical character (at some region of the space) and then reacts at some specific points to stick together on the surface. The continuous addition of ions develops a material deposit connected to the current transient signals measured in electrochemical deposition processes. Unlike current models found in the literature, this procedure avoids the computation of the area covered by the diffusion zones, allowing a formalism skill to describe equally well the absorption of ions by channels on electrified surfaces. The theory is applied to the electrodeposition of nickel on n-silicon and explains the failure of standard three-dimensional nucleation models to reproduce situations where interfacial relations control the dynamics. It is shown that, processes dominated by chemical reactions on the electrode can not be classified as possessing an exclusively instantaneous or progressive character, rather, they mix together these two limiting forms of nuclei activation to defines the current transients in its beginning.