Confined anodic aluminum oxide nanopores on aluminum wires

Anodic aluminum oxide (AAO) nanopores were grown on Al wire, 100 μm diameter in oxalic acid at 20, 40 and 70 V. Total charge passed and wire resistance were monitored as a function of anodization time providing precise Al consumption rates. Inductively coupled plasma optical emission spectroscopy was conducted on the used electrolyte to determine ejected Al3+ ion concentration. Reduced growth rates, lower interpore distances, thicker barrier layer Al2O3 and cracks in the AAO > 10 μm thick were observed. Compared to planar AAO at low current densities, at least 22% higher efficiencies and higher volume expansion factors were obtained. These results were explained on the basis of reduced ionic conductivity and increased viscosity of the barrier layer Al2O3 as a result of circumferential compressive stresses generated due to pore growth on convex surfaces.