Extracting deposition parameters for cobalt–molybdenum alloy from potentiostatic current transients

In a previous paper a model for the potentiostatic current transients during induced cobalt–molybdenum alloy deposition was developed and tested in a few experimental conditions. Hemispherical geometry was assumed for the alloy crystallites. Here the model is studied in a wider range of experimental situations, in which the potential and the molybdate concentration are varied. It is verified that the model can be applied to the new set of variables. However, at the lowest molybdate concentrations the theoretical parameters do not agree with the experimental findings. This is attributed to changes in the geometry of the crystallites, which are conical rather than hemispherical. The consistency of the model in these conditions is also tested. The model correctly predicts that the system tends to follow the pattern found in charge-transfer controlled Co deposition as molybdate concentration in solution decreases. Pure Co without molybdenum was also deposited. SEM images showed that the pure Co deposits have sharp points. In comparison to alloy deposition, which is instantaneous, the pure-Co deposition is progressive. The difference in the nucleation kinetics may be caused by the molybdenum oxide layer, which is deposited before the alloy. The oxide layer may change the electrochemical properties of the substrate and therefore modify the nucleation kinetics.