Abstract
We have observed porous alumina layers fabricated by the anodic oxidation of aluminum sheets utilizing a selective etching. We have found that two types of 3-dimensional structures form inside the alumina layer during the oxidation process. One is dome-like micro-structures which have straight pores of approximately 100 nm in diameter, and the other tree's root-like structures which grew in a radial manner. By using non-uniform etching conditions that the concentration of phosphoric acid is more than 20 wt%, those buried structures appear because the matrix is preferentially removed. Moreover, we have found that the position of the dome-like structures can be controlled by artificial scratches on the initial surface. [DOI: 10.1380/ejssnt.2008.147]
