Potential and Adsorbate Effects in Electrodeposition: Lessons Learned from Atomic-Scale in Situ and Operando Studies

Electrodeposition has become an important tool in nanoscience and -technology. Examples range from metallization processes in the microelectronics industry to self-organized growth of nanomaterials. Because the growth behavior and the resulting deposit morphology can be varied over a wide range by the electrochemical parameters and by suitably chosen additives, electrodeposition often provides superior control as compared to rivaling methods or even enables deposition of structures which are unobtainable by other means. On the other hand, precisely the strong dependence on potential and solution composition poses a problem as they are largely not understood. Development of electrodeposition or electroless plating processes therefore is still largely empirical, specifically for the deposition of structures with well-defined nanoscale morphology. For knowledge-based strategies better understanding of the atomic–scale processes is required. In particular, it is necessary to clarify how the potential-dependent interface structure and the presence of surface-active species influence processes such as diffusion on the planar surface and across steps, nucleation events, and the ion transfer itself.

Such data can be obtained by state-of-the-art surface-sensitive methods, which enable in situ studies of the interface structure and dynamics or even operando investigations at growth rates approaching those in technological processes. Together with ab initio theory calculations they provide first insights into the complex effects of potential and coadsorbates on the dynamics of species at the surface of the deposit during the growth (e.g. metal adatoms). I will specifically present studies of Cu and Au single crystal electrodes by synchrotron-based X-ray scattering techniques and high-speed scanning tunneling microscopy, focusing on the influence of halides on surface dynamics and metal growth. The obtained results reveal very pronounced and partially unexpected effects, which can lead to crossover between qualitatively different growth regimes. The relevance of these observations for electroplating, prospects for operando studies of technologically interesting cases, as well as remaining challenges and future directions will be discussed.