Enhancement of pore size distribution in one-step hybrid pulse anodization of aluminum thin films sputtered on Si substrates

• The target power and substrate bias affect the Al surface morphology.
• Rougher surface due to larger grain size results in non-uniform pore structure.
• Morphology-induced uneven electrical field influences the pore characteristics.
• Electrical field concentration enhances chemical or field dissolution.
• The pore size distribution can be enhanced by improving the surface morphology.

The anodic aluminum oxide (AAO) has attracted more and more researches since its porous structure was discovered for many nano-enabled applications. In this article, the AAO was fabricated by one-step hybrid pulse anodizing the sputtered aluminum (Al) thin films on Si substrates for nanoporous template due to limited thickness. Surface morphology with the varied electrical field can influence the AAO characteristics during anodization process. The various Al target power and substrate bias were performed to form different surface morphology of the sputtered Al thin films which were further investigated for the AAO synthesis quality. The more non-uniform AAO structure was found on the sputtered Al thin films with rougher surface or larger mean grain size which was deposited at high target power or no bias. In contrast, the Al films with smaller mean grain size and smoother morphology deposited at relatively low target power with bias were beneficial for more uniform pore size distribution. On the constant anodizing condition, the pore size distribution can be enhanced with the reduced standard deviation from 13.01 to 6.34 nm by improving surface morphology of the as-deposited Al film.