AAO-assisted synthesis of highly ordered, large-scale TiO(2) nanowire arrays via sputtering and atomic layer deposition

Highly ordered nanoporous anodic aluminum oxide (AAO) thin films were fabricated in oxalic acid under a constant voltage via a two-step anodization process. To investigate the high-aspect-ratio (7.5:1) filling process, both sputtering and atomic layer deposition (ALD) were used to form TiO(2) nanowires. Field emission scanning electron microscopy and high-resolution transmission electron microscopy images indicated that mushroom-like TiO(2) structures were sputtered onto the AAO template surface, and the ALD-coated TiO(2) exhibited fine filling results and clear crystal grain boundaries. Large-scale and free-standing TiO(2) nanowire arrays were liberated by selectively removing the aluminum substrate and AAO template via a wet etching process with no collapsing or agglomeration after the drying process. ALD-deposited TiO(2) nanowire arrays that were 67 nm in diameter and 400 nm high were transferred from the AAO template. The ALD process enabled the rapid, simple synthesis of highly ordered TiO(2) nanowire arrays with desired parameters such as diameter, density, and thickness determined using diverse AAO templates.