We describe the formation of long, highly ordered arrays of planar oriented anodic aluminum
oxide (AAO) pores during plane parallel anodization of thin aluminum ‘finger’
microstructures fabricated on thermally oxidized silicon substrates and capped with a silicon
oxide layer. The pore morphology was found to be strongly influenced by mechanical
constraint imposed by the oxide layers surrounding the Al fingers. Tractions induced by the
SiO2 substrate and capping layer led to frustrated volume expansion and restricted oxide flow along the interface, with extrusion of oxide into the primary pore volume, leading to the
formation of dendritic pore structures and meandering pore growth. However, partial relief of
the constraint by a delaminating interfacial fracture, with its tip closely following the anodization front, led to pore growth that was highly ordered with regular, hexagonally packed
arrays of straight horizontal pores up to 3 um long. Detailed characterization of both straight and dendritic planar pores over a range of formation conditions using advanced microscopy
techniques is reported, including volume reconstruction, enabling high quality 3D
visualization of pore formation.