In Situ Determination of the Pore Opening Point during Wet-Chemical Etching of the Barrier Layer of Porous Anodic Aluminum Oxide: Nonuniform Impurity Distribution in Anodic Oxide

Wet-chemical etching of the barrier oxide layer of anodic aluminum oxide (AAO) was systematically investigated by using scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and a newly devised experimental setup that allows accurate in situ determination of the pore opening point during chemical etching of the barrier oxide layer. We found that opening of the barrier oxide layer by wet-chemical etching can be significantly influenced by anodization time (tanodi). According to secondary ion mass spectrometry (SIMS) analysis, porous anodic aluminum oxide (AAO) samples formed by long-term anodization contained a lower level of anionic impurity in the barrier oxide layer compared to the short-term anodized one and consequently exhibited retarded opening of the barrier oxide layer during the wet-chemical etching. The observed compositional dependence on the anodization time (tanodi) in the barrier oxide layer is attributed to the progressive decrease of the electrolyte concentration upon...