Abnormal Anodic Aluminum Oxide Formation in Confined Structures for Lateral Pore Arrays

We report on abnormal behavior in anodic oxidation of Al in mechanically confined structures for formation of horizontal nanoporous anodic alumina oxide (H-AAO). Instead of smooth pore walls, periodic dendrite inner pore structures form, the growth rate is suppressed to 5% of its value during bulk anodization under the same conditions, and a steady-state is never reached. These anomalies associated with H-AAO originate from suppressed volume expansion and a plastic flow of confined by the hard mask. By determining new anodization conditions leading to zero volume expansion, dendritic H-AAO can be avoided and kinetic retardation minimized.