Fabrication of gold nanotip array using anodic aluminum oxide (AAO)

Abstract

Nanotip has been widely researched due to its interesting properties, such as field emission, electromagnetic field enhancement, etc. It has been used in applications such as storage material and scanning tunneling microscope (STM) imaging. Most recently, Stockman has proposed that a large electromagnetic field enhancement is possible at the tip, open an opportunity to develop a highly sensitive sensor. However, most of the tips are fabricated using method such as reactive ion etching (RIE), focused ion beam (FIB) or electrochemical etching. These conventional methods not only required expensive equipments (RIE & FIB) and involved many processes, but also limited to the choice of materials. Hence this project seeks to use AAO template as an alternate fabrication method.

The AAO template was successfully fabricated using 2 acid anodization. The pore diameter was controlled with the manipulated of voltage and electrolyte during anodization. The barrier layer was then removed using phosphoric acid and the etching duration has been optimized to effectively remove the barrier layer without over compromising the apex of the template.

Gold was electrodeposited into the open-through hole AAO nanotip array template with precision time control. Au nanorod array can be fabricated if the deposition time is insufficient, while “mushroom” like structure can be obtained when there is excessive deposition time. Finally, an ordered nanotips array was successfully fabricated with the apex diameter and base diameter of 34nm and 210 nm respectively. This method is considered comparable to the conventional method. In addition, the structure of the nanotip array can be varied by controlling the voltage together with the anodization time. With this novel approach, the materials choice of the nanotip array is not limited and will be very important for the future nanotechnology industry.