Growth of gold fractal nanostructures by electrochemical deposition in organic electrolytes: Morphologies and their transitions

We have studied the growth of gold fractal nanostructures by a novel electrochemical deposition (ECD) method. In our ECD process, instead of an aqueous solution of metallic salt, we use an organic solution (such as N,N-dimethylformamide (DMF) or acetonitrile) as the electrolyte and integrate the microscale ECD system into the SiO2/Si chip. Quasi-two-dimensional gold fractal nanostructures can be formed using the organic electrolyte. The morphology of the deposit strongly depends on the kind of organic electrolyte that has been used. A diffusion-limited aggregation (DLA) pattern can be formed in DMF. While in acetonitrile, aside from the DLA pattern, a variety of other typical morphologies can be identified, and they appear in consecutive, patterns varying from a DLA fractal, to a dense branching morphology (DBM), to a ramified structure. In some cases the ramified structures can even evolve into nanoscale dendrites or nanowires. To the best of our knowledge, these phenomena have not been reported before. We propose a qualitative explanation for these phenomena based on the mass transfer equation and discuss possible applications of these nanostructures.