Fabrication of Dome-Shaped Porous Alumina Microstructures Using Patterned Aluminum Substrates

Abstract

Porous alumina is widely used as template for making nanosized materials including nanodots, nanotubes, and nanowires, because of its well-aligned pores. The introduction of microscaled patterns onto the initial aluminum surface facilitates the fabrication of dome-shaped porous alumina microstructures with vertically aligned nanopore arrays. A pre-patterned aluminum substrate fabricated by the imprinting method is anodically oxidized in oxalic acid, and then selectively etched in phosphoric acid. The etching rates of the porous alumina membrane vary regionally, which has been attributed to the structural non-uniformity of the nanoporous membranes. The imprinting method can produce highly ordered dome-like porous alumina microstructures at desired positions; however, it is difficult to achieve these microstructures over a large area. In this work, we obtained various three-dimensionally dome-shaped porous alumina microstructures, which are called simply microdomes, at desired positions by means of the stamping method over a large area. Furthermore, we investigated the effect of the anodization temperature on the formation of microdomes, resulting in increasing aspect ratio at high anodization temperature.