Nucleation and growth mechanism of CdTe at polycrystalline gold surfaces analysed through Δm/t simulation transients

The nucleation and growth mechanisms of cadmium telluride have been investigated in aqueous H₂SO₄ solution using polycrystalline gold as substrate. Using cyclic voltammetry as a reference, a series of potential steps experiments were performed in order to simulate the corresponding j/t experimental transients that gave only a current decay proportional to t^-1/2. Conducting the potential steps in an electrochemical quartz crystal microbalance (EQCM) allowed recording Δm/t transients that were potential dependent. Introducing some modifications in the classic equations of the nucleation and growth models, these transients gave information about the mechanism of CdTe electrocrystallization. It is proposed that the initial process is associated with the nucleation and growth of the Te islands followed by fast formation of Cd islands and that CdTe is formed through the slow diffusion of these islands. The slow rate of this process was evidenced through the time elapsed before observing a cathodic photocurrent when the electrode surface was illuminated. Gold surface has an influence on the nucleation mechanism favouring the instantaneous over the progressive, specially at more negative values of the final potential step. These results show that Δm/t transient simulations are a suitable tool for studying NGM when convolution of the classical j/t transients does not allow extraction of the appropriate information.