Double-layer PAA with different pore sizes and its growth kinetics based on anodizing current curves

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• The field-assisted dissolution theory (FADT) has been insufficient to explain the observed relationships between porous morphology and current-time curves in porous anodic alumina (PAA).
• Previous interpretations of PAA growth kinetics have been controversial, lacking a comprehensive theoretical framework.
• Understanding PAA formation is crucial for applications in nanotechnology and materials science.

Purpose of the Study:

• To clarify the controversial growth kinetics of porous anodic alumina (PAA).
• To explain the relationship between porous morphology and current-time curves using fundamental current theories.
• To challenge the limitations of the traditional field-assisted dissolution theory (FADT) in interpreting PAA formation.

Main Methods:

• Fabrication of double-layer PAA structures with varying pore sizes using multi-step anodization processes.
• Analysis of current-time curves generated during the anodization process.
• Application of ionic and electronic current theories to interpret the observed phenomena.

Main Results:

• The study demonstrates that FADT cannot adequately explain the observed current-time curves and porous morphology.
• Ionic current under high electric fields drives rapid oxide growth, causing current decline.
• Electronic current promotes pore embryo formation and maintains stable pore growth through oxygen bubble evolution.

Conclusions:

• The growth kinetics of PAA are clarified by analyzing ionic and electronic current contributions.
• Constant electronic current facilitates oxygen evolution and pore formation, while constant ionic current supports oxide growth and channel elongation.
• The rate of channel growth, driven by total current, significantly exceeds the field-assisted dissolution rate.