Influence of surface pre-treatment in the room temperature fabrication of nanoporous alumina

In nanoporous alumina, surface pre-treatment, prior to the anodization process, plays a crucial role in the pore structure formation and organization. In this work we employ different pre-treatments to determine the best suited for the subsequent anodization process. We observed significative differences in the current density transients (monitored during anodization), depending on the pre-treatment used. For diamond paste polished surface, scanning electron microscopy (SEM) images of the first anodization revealed a degraded porous structure, with no organization. Samples with NaOH soft chemical etching, ion milling etching and electropolishing pre-treatments revealed the best quality first anodization surfaces, so that a second anodization. process was applied. Current density transients, together with SEM images, showed that there was still growth competition for the ion-milling and electropolishing cases and longer first anodization times are thus required to obtain the equilibrium structure. We show that only in the case of NaOH soft chemical etching, the dimples carved in the aluminum foil from the first anodization step, strictly guide the growth of pores during the second anodization step. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim