Differential equations describing the evolution of defect concentrations inside ultra-thin films are developed and numerically resolved for the growth of passivating films under transient galvanostatic conditions. For this, the injection and recombination of defects together with the increase of the film thickness are taken into account. In the simulation, the defect concentrations pass through a maximum during the growth and increase with the current, becoming independent of it for higher values. To obtain reasonable values of defect concentrations the work shows the need to consider that only a part of the current is used in defect generation. For the film, the specific ionic resistivity passes through a minimum and the overpotential increases almost linearly with thickness. Analysis of the transients leads to the idea that the recombination rate constant can depend on the current density. All these aspects are analyzed and discussed from a physical point of view.
simulation; galvanostatic transients; passivating films; defect concentration; ionic resistivity
