Advancing Nanopore Technology: Anodic Aluminum Oxide Membranes with Anisotropic Pores through Controlled Stretching for Applications in Nanopatterning

In recent years, anodic aluminum oxide (AAO) membranes have been widely used as attractive nanoporous materials because of their applications in drug delivery, membrane filtration, and catalysis. Although AAO membranes with anisotropic pore shapes can be achieved, the methods are often complex and costly. In this work, we present an innovative approach to fabricating AAO membranes with controlled pore geometries, focusing on the transition from nonelliptical to elliptical nanopores. Utilizing commercially available aluminum foils of varying thickness and purity, the research demonstrates a cost-effective and scalable method for producing these specialized AAO membranes. The process involves a two-step anodization, where the aluminum foils undergo electropolishing, anodization, and chemical etching, followed by a unique stretching technique that transforms circular concavities into elliptical shapes. This approach successfully produces elliptical AAO membranes with varying pore sizes and aspect ratios, controlled by different electrolytes and pore-widening times. The study further explores the application of these membranes in nanopatterning by creating anisotropic polymer nanorod arrays using polystyrene (PS) and poly(methyl methacrylate) (PMMA), demonstrating the practical utility of the fabricated AAO membranes in nanomaterial synthesis. The research highlights the potential of the stretching approach in AAO membrane fabrication, promising a diverse range of applications in material science and engineering, particularly in fields requiring precise nanopore geometries.