Optical Super‐Localisation of Single Nanoparticle Nucleation and Growth in Nanodroplets

The formation of metal nanoparticles (NPs) on surfaces by electrodeposition is of significant interest, particularly with a view to understand the early stages of nucleation and growth. Here, the combination of scanning electrochemical cell microscopy (SECCM) and interference reflection microscopy (IRM) is demonstrated to be a compelling approach for real‐time monitoring of NP dynamics within the SECCM meniscus‐electrode wetted area, through synchronous monitoring in the millisecond range of the electrochemical and optical signatures. Diffraction‐limited entities, undergoing phase changes at the electrode substrate, are readily highlighted and tracked in time, including the onset time for the appearance of NPs and their movement over time. The results strongly implicate the rapid formation, surface diffusion and aggregation of smaller entities (not detectable optically) to produce the larger electrodeposited NPs. By applying SECCM tips of different size, it is also possible to understand how the wetted area (meniscus size) plays a key role in the number of NPs formed, with small tip sizes allowing the formation of single NPs. The SECCM‐IRM approach is expected to be a powerful platform for the study of myriad phase‐formation processes at the nanoscale, particularly by drawing on the possibility of making hundreds or thousands of measurements in fresh surface locations through SECCM technology. Electrodeposition of limited number of nanoparticles requires confinement within nano‐electrochemical cells. Super‐localization optical microscopy reveals operando the process dynamics: within the first 3–13 ms the delayed formation of one to six distinct nanoparticles is detected per droplet; later the displacement of their centroid suggests the importance of aggregation and surface diffusion.