Abstract
Electrodeposition is a key technique for fabricating ultra-thin copper foils, where grain refinement plays a critical role in determining their mechanical performance. In recent years, the unique cavitation effects associated with ultrasonic fields have demonstrated significant potential in modulating metal deposition. This study quantitatively investigates the influence of ultrasonic amplitude on the nucleation behavior of copper electrodeposited on a Co-Ni alloy substrate. At amplitudes of 18-24 μm, ultrasound enhances ion transport and activation via cavitation and agitation, thereby accelerating nucleation. As the amplitude increases, high amplitudes (30-42 μm) intensify acoustic streaming and cavitation bubble clustering, inducing strong fluid perturbations at the cathode interface. That brings local current pulsation and intermittent deposition. These dynamic effects promote finer grain structures and more uniform grain distribution. Notably, at 42 μm amplitude, the grain size is reduced by nearly an order of magnitude. These findings provide quantitative insights into ultrasonic regulation, offering guidance for high-efficiency, uniform copper foil deposition.