Nanoporous anodic alumina obtained without protective oxide layer by hard anodization

In this study, a fast and cost-effective approach is applied for fabricating nanoporous anodic alumina membranes under hard conditions without a protective oxide layer. This structural characteristic is a result of using a two-step anodization strategy under specific hard conditions during the second anodization step (i.e. high stirring rate, low acid electrolyte temperature and concentration). Notice that, after the anodization process, the membrane is detached from the aluminium substrate at the same time that pores are opened. So, after the fabrication process, no additional stages are required for removing both the protective oxide layer and the oxide barrier layer from the top and the bottom of the membrane, respectively. The resulting nanostructures obtained by this approach are defect-free nanoporous anodic alumina membranes with well-defined pores from the top to the bottom. This makes it possible to directly use those membranes in later applications (e.g. templates for replicating nanostructures, filters, optoelectronic devices and so forth) without additional processes and costs.

► Nanoporous anodic alumina under hard conditions without a protective oxide layer. ► Two-step anodization under specific hard conditions during second anodization step. ► Membrane detachment from aluminium substrate at the same time that pores are opened. ► Defect-free nanoporous anodic alumina membranes with well-defined pores. ► Direct use of those membranes in later applications without additional costs.