Surface and interface characterization of nanoporous alumina templates produced in oxalic acid and submitted to etching procedures

High purity aluminum (Al) sheets were used to produce ordered nanoporous alumina templates by two step anodization technique using oxalic acid as electrolyte. Electrochemical polishing of Al sheets was performed in order to study the surface roughness influence on the pore roundness of the alumina templates. The templates were submitted to progressive reduction of anodizing voltage (electrochemical etching) to thin the Al₂O₃ barrier layer on the bottom of the pores, and to chemical etching to widen the diameter of the pores. The pore diameter and porosity increase linearly with the chemical etching time, while interpore distance, circularity, pore density and pore distribution do not change. Electropolished Al substrates produce nanoporous Al₂O₃ templates with more circular pores, and the Al₂O₃ barrier layer at the Al₂O₃/Al interfaces is completely removed after the electrochemical and chemical etching processes.