Abstract
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 TiO2 nanowires. Field emission scanning electron microscopy and high-resolution transmission electron microscopy images indicated that mushroom-like TiO2 structures were sputtered onto the AAO template surface, and the ALD-coated TiO2 exhibited fine filling results and clear crystal grain boundaries. Large-scale and free-standing TiO2 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 TiO2 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 TiO2 nanowire arrays with desired parameters such as diameter, density, and thickness determined using diverse AAO templates.
Highlights
One-dimensional TiO2 thin films with nanoscale structures, such as nanotubes, nanorods, and nanowires, present a variety of applications, including catalysis [1,2,3], gas sensing [4,5], and energy harvesting [6,7], due to their large surface-to-volume ratio, convenient band gap, and quantum confinement effects
The surface color for the atomic layer deposition (ALD)-coated anodic aluminum oxide (AAO) template changed, while the sputtered AAO template remained unchanged. This macroscopic phenomenon primarily resulted from the multilayer interference effect [21], which indicated that the ALD-coated TiO2 yielded better filling than the sputtering process
TiO2 nanowire arrays were fabricated via ALD by separately removing the aluminum substrate and AAO template via wet etching
Summary
One-dimensional TiO2 thin films with nanoscale structures, such as nanotubes, nanorods, and nanowires, present a variety of applications, including catalysis [1,2,3], gas sensing [4,5], and energy harvesting [6,7], due to their large surface-to-volume ratio, convenient band gap, and quantum confinement effects. An controlled template-assisted growth method has drawn significant interest because the template can be used to directly form a desired nanostructure. Using a template with a specified shape, diameter, density, and arrangement allows a large number of desired targets to be duplicated once the specific template structure has been formed. Even large-scale films can be prepared via a template synthesis.
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