Formation of Bottle-Shaped Pores with Petaloid Shoulder within Anodic Alumina

Abstract

Porous anodic alumina (PAA) with distinct bottle-shaped pore channels was fabricated through annealing, reanodisation and chemical etching from phosphoric acid PAA. The effects of annealing at the elevated temperature up to 600°C on the subsequent treatments have been explored to obtain largest differential diameters of the two sections. It is shown that the structural change in the barrier layer induced by annealing at 500°C can be reversed by reanodisation, which is crucial for the fabrication process. Under proper conditions, the diameters of the two sections obtained are about 345 and 220 nm, respectively. Potential applications of such PAA include nano-structured material synthesis and through-hole membrane fabrication. Petaloid shoulder consisting of regular ridges and depressions was clearly revealed in the transition region, which can be attributed to the structural variation induced by a non-uniform electric field around the barrier layer within each cell. The redistribution of the space charge during annealing may enhance the variation of the electric field and hence preferred etching.