  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.
