Fabrication of high aspect ratio copper nanowires using supercritical CO2 fluids electroplating technique in AAO template

This study utilizes the supercritical and post-supercritical electroplating technique, to fabricate copper nano-wires inside ultra-high aspect ratio Anodic Aluminum Oxide templates (AAO templates). Comparisons of the electroplating capabilities and results were made between these methods and the more common traditional electroplating techniques. Under identical experimental conditions and on ultra-high aspect ratio AAO template with thickness of 60 µm (aspect ratio of 1:490), it is evident from the results that the supercritical electroplating process has the fastest electroplating velocity of the three processes (~1.33 µm/min), followed by post-supercritical electroplating (~1 µm/min) and traditional electroplating is the slowest (~0.67 µm/min). This study also discusses the electroplating quality of the copper nano-wires. Samples were sliced along the cross-section, and Field Emission Scanning Electron Microscopy (FESEM) was utilized to observe the copper nano-wires. X-Ray Diffraction (XRD) was used to observe that the crystal structures is polycrystalline, and with the use of equations it is determined that grain size will not be severely affected by changes in current density and supercritical pressure in themselves, but instead the different processes do produce an evident change. The grain size achieved with supercritical electroplating is the smallest, followed by the post-supercritical electroplating, and the largest was given by the traditional electroplating process. Through these results it can be proved that supercritical electroplating process indeed provides grain refinement capabilities. The supercritical fluid-enabled electroplating process utilized for these experiments does not need addition of any surfactants to aid filling of the structures, but only relies on the intrinsic properties of supercritical fluids to achieve complete filling of nano-holes, and because there are no surfactants, we can achieve higher degree of purity in the copper nano-wires.