Mechanism of isolated pore formation in anodic alumina

Local anodization of aluminum was studied by patterning SiO2 masks on aluminum thin films by nanoimprint lithography and subsequent electrochemical anodization. We observed the formation of isolated pores when the mask openings are of the order of the steady-state unpatterned pore spacing, which is related to the breakdown strength of the alumina and the anodization potential. Based on our observations, we have developed an empirical model describing the formation mechanism of porous aluminum oxide. The model described successfully explains the formation and shapes of pores as a function of mask aperture size.