Realizing Structural Coloration via Lamellar Nanostructures Formed by Precise Mechanical Patterning and Selective Etching of Metal Multilayer Films

Structural coloration, originating from nanoscale interactions of light with engineered surfaces, delivers tunable color features and application potential in anti-counterfeiting compared to conventional dye-based methods. In this study, a fabrication strategy for structural color surfaces is presented by integrating ultra-precision mechanical patterning with selective wet etching of Al/Cu multilayer thin films. By precisely adjusting the cutting load, the number of exposed Cu layers is controlled, enabling the formation of single-layer lamellar (SLL) and double-layer lamellar (DLL) nanostructures. Subsequent wet etching selectively removed the Cu layers, further refining the lamellar geometry. Optical characterization revealed that DLL structures exhibited vivid, angle-independent blue coloration, while SLL structures showed angle-dependent spectral variations. Chromaticity analysis quantitatively confirmed the correlation between the lamellar architecture and the resulting optical behavior. Additionally, directional structural color patterns with orientation-dependent visibility are successfully demonstrated, which highlights their potential for multi-level optical security applications. To further improve durability, conformal Al₂O₃ encapsulation by atomic layer deposition is applied, preserving the optical response while enhancing environmental stability. This work offers a practical and scalable approach to customizable structural color devices, supporting their use in nanophotonic applications and advanced anti-counterfeiting technologies.