Grazing Incidence X-ray Total Scattering Reveals the Effect of the "Two-Step" Method for the Anodization of Aluminum Surfaces.

Thanks to its ability to form a lattice of self-ordered nanosized pores, nanoporous anodic aluminum oxide (NP-AAO) is a promising material with diverse applications, for example, as membrane for the controlled deposition of catalysts. NP-AAO is obtained by the anodization of an aluminum substrate under specific pH and voltage conditions. However, the growth mechanism of the oxide is still under debate. We shed light on this process by investigating structural changes at the atomic scale using pair distribution function (PDF) analysis. We thus performed X-ray total scattering experiments under grazing incidence conditions during the anodization of aluminum substrates exhibiting different crystallographic facets. By doing so, we were able to track the evolution of the local structure of aluminum oxide species forming at the oxide-electrolyte interface over time.