The mechanism behind the selective metal nanoscale etch method for precise metal nanopatterning

This paper reports for the first time the exact mechanism of the selective metal nanoscale etch method (SMNEM), which is a simply controllable and cost-effective approach for metal nanoscale etching and size reduction. This method is based on the galvanic displacement, Kirkendall effect, and selective etching. The size reduction is linearly controlled by the galvanic displacement in the early stage (1 min). In the later stage, a Kirkendall void is formed between the Ni and Au layer, which is well understood from Fick's law of diffusion. As matching with the experimental results, Ni nanowires with 30 +/- 4 nm width and 50 +/- 7 nm height were easily fabricated from nanostructures with 150 +/- 3 nm width and 110 +/- 2 nm height. The morphology and position of the Ni nanostructures are all predetermined by their initial conditions. Also achieved was the fabrication of complicated three-dimensional nanostructures such as Au nanowires and nanochannels from reduced Ni nanowires by a full replacement reaction.