MECHANISMS AND APPLICATIONS OF THE ELECTROCHEMICAL FORMATION OF NANOPATTERNS

Abstract

Surface nanofabrication is the art of making novel materials with surface features or patterns smaller than 100 nm. To this end, various techniques have been proposed, e.g. optical/ electron lithography, Langmuir Blodgett films, Dip-pen lithography, block co-polymer templates, and ion irradiation. However, each technique has its own inborn limitation, whether time-consuming or expensive or lack of resolution. In this thesis, the author describes a cheap and time-efficient alternative to generate nanopatterns on several transition metals, alloy, and silicon via electrochemical methods and provides more insight into the mechanism that leads to the formation of these patterns. Self-organized nanopatterns discovered on electropolished vanadium include dots (called pimples), labyrinths (interconnected elongated pimples), and valleys (called dimples). The window for these patterns to occur is extremely small. A little (0.1%) variance of the electrolyte composition can lead to pattern transition. A time evolution of patterns, from a flat surface to pimple pattern to labyrinth pattern to dimple pattern, has been observed as well. The author also found out that dimple pattern can be achieved on tantalum via electropolishing and nanotubes can be fabricated by anodization. The relative amount of HF and water in the electrolyte is the key that controls the switch between these two patterns. The author has extended the formation of dimples from pure metals to a biomedical alloy (Ti-6Al-4V). Since the size of the dimple pattern is on the same scale as cell features, this dimpled alloy has great potential in biomedical implantation. Last but not least, this thesis explores the pattern formation on silicon, a semiconductor, via electropolishing, which is thus proven to be a universal nanopatterning technique. This thesis opens a route to nanopatterning metals, alloys, and semiconductors via electropolishing, while making a contribution to a deeper understanding of the mechanisms behind the formation of these patterns.