Self-organization of anodic aluminum oxide layers by a flow mechanism

Abstract

Anodic oxidation of aluminum in solutions that dissolve the amorphous oxide produces films with hexagonally-ordered patterns of pores. We show using linear stability analysis that an anodization model including viscous oxide flow accurately predicts the scaling relation governing pore spacing. Flow is driven by nonuniform compressive stress near the oxide-solution interface, resulting from anion adsorption on surface growth sites. The interfacial stress layer is approximated as surface stress, leading to analogous instability mechanisms as in the surface-tension driven Marangoni instability of thin liquid films.