The effect of rf-irradiation on electrochemical deposition and its stabilization by nanoparticle doping

Qualitative observations of electrochemical deposition in thin circular cells have shown that radio-frequency (rf) irradiation of zinc sulfate solutions can dramatically affect the deposition patterns. For some growth parameters the rf-treatment can even induce morphology transitions between the dense branching morphology and dendritic growth. We found that the effects of rf-treatments can last for a long time (hours). In addition, detailed studies using electron microscopy observations reveal that the effects span on all scales, from the micrometer-scale organization to the self-organization of the macroscopic pattern. We propose that these changes of patterning on all scales resulted from singular effects of gas-filled submicrometer bubbles or nanobubbles, which are generated by the rf-irradiation. The idea is that hydration shells around the nanobubbles induce water ordering that acts as a new singular perturbation mechanism in the solution. The latter is in addition to the well studied microscale singular perturbation mechanisms in the deposit (surface tension and attachment kinetics). We also studied electrochemical deposition in zinc sulfate solutions prepared from water that is doped with nanoparticles under rf-irradiation, and found similar and even amplified effects. Moreover, the nanoparticle doping stabilizes the effects-they are retained months after the solutions were prepared.