Fabrication of tunable Large-Area Moth-Eye nanostructures for antireflection and hydrophobicity via anodic aluminum oxide templates and nanoimprint lithography

Abstract

In this study, a comprehensive process–structure–function roadmap was established for bio-inspired functional surfaces. We systematically controlled the pore diameter, interpore distance, pore depth, and pore aspect ratio of anodic aluminum oxide (AAO) master templates via multistep anodization. These templates were then replicated in durable nickel–cobalt alloy working molds through electroforming, and their nanostructures were transferred to polycarbonate films using nanoimprint lithography. Our findings highlighted the critical influence of pre-anodization, electrolyte type (oxalic acid for an ~ 100 nm interpore distance; phosphoric acid for ~ 400 nm), anodization potential, and time on the AAO structures. We also identified 100 A/m² as the optimal current density for achieving high-aspect-ratio structures under intense anodization. The polymer film replicas obtained using these precisely controlled templates showed significantly enhanced functional properties: the average surface reflectance decreased from 10.85% to a minimum of 3.5%, transmittance increased from 80.1 to 92.3%, and water contact angles improved from 91.46 to 138.69°. Thus, a higher structural aspect ratio is crucial for enhanced hydrophobic performance, consistent with the Cassie–Baxter model. In summary, this research provides an efficient, controllable method for manufacturing high-performance bio-inspired functional surfaces and, more critically, establishes direct correlations between anodization parameters and the resulting optical and wetting properties, offering key guidance for material design.