Ni Nanostructures Formed via pH-Dependent Corrosion-Redeposition of Thin Nickel Films in Glycine-Based Solutions

Nickel (Ni) is an interesting material for several applications, due to qualities including resistance to high temperature, oxidation, and corrosion, which are also present at the nanoscale. In particular, Ni nanowires show many applications in biology, optical devices, solar cells, and sensors, among others. Ni nanostructures have been created so far using a variety of methods, including hydrothermal, laser ablation, and chemical vapor deposition techniques. In this study, we investigate the fabrication of Ni nanostructures via local corrosion of thin Ni films deposited by physical vapor deposition. Slow Ni corrosion is achieved using water, glycine, and calcium chloride static solutions with various pH levels. After a considerable amount of time (24-48 hours) of contact between the Ni film and the solution, micron-sized, roughly circular isotropic corrosion patterns are observed. Scanning Electron Microscopy (SEM) images show that nanostructures form inside the corrosion patterns. Typically, a nanowire-like structure extends vertically from the center of most patterns; for those with larger diameters, very thin planar nanowires extend from this central structure. SEM-based Energy Dispersive Spectroscopy measurements reveal that the central nanostructure is made of Ni, while the composition of the thinner, planar nanowires cannot be resolved using this technique. Our findings via simulations suggest a process of corrosion starting at specific locations such as film defects, with subsequent Ni redeposition due to a radial Ni concentration gradient at the metal film-solution interface. Further studies should determine if this process can be made controllable as a new synthesis process of Ni nanostructures.