  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 porous anodic alumina
(PAA) structure has been deeply investigated, as well as the electrolyte
temperature, the number of potential steps and the exponential decay rate. The
results presented herein evidence that straight pores can be obtained and
simultaneously remove the dielectric layer in spite of applying the exponential
voltage decay during the PAA synthesis, through a smart adjustment between the
anodization conditions and exponential voltage decay parameters. Additionally,
the PAA structure can be tuned to fabricate hierarchically nanoporous templates
with secondary pores ranging from 2 up to 10 branches. The presented simple
procedure aims to become a standard step for the fabrication of the next
generation PAA templates based devices.
