Characterizing and optimizing the electropolishing and pore arrangement in porous anodic aluminum oxide (AAO)

Abstract

The effect of surface roughness of aluminum on pore arrangement of anodic aluminum oxide (AAO) has been studied. Level crossing analysis was used in order to quantitatively evaluate the surface roughness (smoothness) of aluminum which was electropolished under a wide range of different voltages, temperatures and times, using $$\tt \normalsize H_3PO_4+H_2SO_4+H_2O(4:4:2, v/v)$$ electrolyte. We present an image processing method which quantitatively determines the pore arrangement of AAO nanostructures which were formed in 0.3 M oxalic acid via two-step self-organized anodization, at 1 °C at constant voltage of 40 V. Here, we have analysed AAO which naturally forms hexagonal structures. However, the image processing method we have proposed here can be used basically to analyse any periodic structure. We have shown that the pore arrangement of AAO is in direct correlation with surface roughness and the best arrangement in AAO can be achieved for the smoothest surface, i.e. lowest value of level crossing.