Artwork-like multicolor structural coloration via spatially patterned anodic aluminum oxide with uniform-cavity design

Conventional dye-based color filters suffer from limited chemical stability and environmental durability. Structural color technologies that exploit nanophotonic phenomena offer a promising alternative; however, fabricating intricate nanostructures and multicolored patterns over a large area remains a significant challenge. Here, we present a scalable approach to artwork-like coloration by using spatially patterned anodic aluminum oxide (AAO) as the dielectric layer in metal-insulator-metal (MIM) cavities. Local modulation of the anodization conditions on a single aluminum film allows precise engineering of the effective refractive index values of the AAO layer. This introduces a conceptual shift: resonance is decoupled from geometrical factors and governed instead by porosity-driven refractive index modulation, a new design lever for nanophotonics. Consequently, diverse color domains are generated within a single cavity profile, enabling planar integration. Artwork-like multicolor patterns with aesthetic and functional impact are achieved on centimeter-scale substrates, and, because anodization is already an industrially established large-area process (used even in aircraft components), the method is inherently scalable to much larger surfaces.