Novel Pre-oxidation Patterning on Thin Aluminium Film Generating Ordered Nanopores through Anodization

Abstract

Anodic Aluminum Oxide (AAO) is widely employed as a template for fabrication of nanowires and nanotubes due to its ability to generate self organized (SO), well ordered pore structures. We have developed a new aluminum pre-patterning technique to create well ordered nanopore arrays on thin films deposited on silicon substrates. We form patterns of thicker oxide on the surface via local oxidation process using a conducting Atomic Force Microscope (AFM) tip working in contact mode. Pores are forced to nucleate between the pre-oxidized regions during the anodization process. The relation between applied voltage and ordered interpore distance has been found to be linear for these supported thin films. However, the pore spacing is highly reduced compared to free standing foils. A new empiric law has been confirmed for a wide range of voltages, solution concentrations and different electrolytes, including oxalic and phosphoric acid. Our results show that pre-oxidation patterning is an alternative technique to achieve an ordered nanoporous template through the anodization process.

Electrochemical engineering of hollow nanoarchitectures: pulse/step anodization (Si, Al, Ti) and their applications

“…84,85 The electric field is focused at the concave centers acting as nucleation points for the pore growth. [86][87][88][89] Matching the patterned pitch with the correct applied voltage is crucial in the process since it prevents the holes from nucleating and developing outside of the pre-textured patterns. Comparing with the patterning techniques such as focused ion beam, 75,90 mechanical micro-machining 91 or nanoindentation, 92 the anodic pre-texturing gives a similar patterning effect with a low cost.…”

“…31,74,86,99 By separating the anodic protocol into two, the process that pre-texturing is sorted as a first step and further anodization as second step lead to a highly self-assembled hexagonal pattern arrangement. [87][88][89] The pretextured concave patterns are generated on Al surface in 0.3 M oxalic acid solution after removing top oxides in a mixture of H 3 PO 4 (6.0 wt%) and H 2 CrO 4 (1.8 wt%). This pre-textured specimen is further anodized for 5-60 s to achieve a nanodot array master mold with a pitch of about 100 nm and height/depth of 90 nm for photonanoimprinting.…”