The morphology and nucleation kinetics of copper islands during electrodeposition

We describe a study, using in situ transmission electron microscopy, of the shape and nucleation kinetics of three-dimensional islands formed during the electrochemical deposition of copper. By operating an electrochemical cell within an electron microscope, we obtain real-time images of the formation of copper islands on a gold electrode while simultaneously recording electrochemical data such as voltage and current. We first present cyclic voltammetry, where the images show the deposition and stripping processes while the voltammogram demonstrates qualitatively the regimes in which diffusion and surface reaction are the rate limiting steps. We then examine island growth quantitatively under conditions of constant potential. Images recorded during growth at various potentials allow direct visualization of the differences between island shapes in the diffusion limited and kinetically limited growth regimes. Furthermore, a combined analysis of the current transients and the images allows parameters such as the diffusion coefficient, the rate constant and the critical nucleus size to be determined. We discuss these results in the context of electrochemical nucleation and growth models.