Microscale steps and micro–nano combined structures by anodizing aluminum

In this paper, we firstly present a novel microscale-step structure fabricated by anodizing aluminum in a mixture of 0.05–0.5 wt% NaCl (HCl), 2 wt% H3PO4 and 20 wt% ethanol under potentials of 1–40 V at room temperature. Then, we present two micro–nano combined structures by integrating the microsteps with nanopores through multi-step anodizations. The microstep–nanopore hierarchical structure was obtained by re-anodizing the sample in oxalic acid, and the regular nanopores can be realized on the microscale patterned aluminum surface. The two-layer porous structure was one layer of nanoporous anodic alumina and another layer of micropores by two-step anodization on sampleʹs both sides. These two novel structures can be useful for surface engineering and high flux filtration, respectively. The current fabrication approach broadens the applications of aluminum anodization, and brings a new method for assembling micro–nano structures.