Fabrication of porous anodic alumina (PAA) templates with straight pores and with hierarchical structures through exponential voltage decrease technique

The present work aims to become a standard step for the fabrication of the next generation porous anodic alumina (PAA) templates based devices and to provide new insights on the mechanism involved in the porous anodic alumina formation. The oxide barrier layer at the bottom of the pores has been successfully thinned by applying an exponential voltage decrease process followed by a wet chemical etching. The impact of the potential drop on the PAA structure has been deeply investigated, as well as the electrolyte temperature, the number of potential steps and the exponential decay rate. The presented results underline that a smart adjustment between the anodization conditions and exponential voltage decay parameters can simultaneously give PAA structures with straight pores and remove the dielectric layer in spite of applying the exponential voltage decay step. Additionally, the PAA structure has been tuned to fabricate hierarchically nanoporous templates with secondary pores ranging from 2 up to 10 branches.