Novel durable broadband absorber with hierarchical nano/micro photonic structure

This study presents an innovative fabrication method that integrates chemical bath etching and anodization to produce a hierarchical nano/micro-structured surface on aluminum substrates. The proposed methodology is simple and uses conventional equipment and chemical components, generating quasi-crystalline nanostructures over a large area of several cm${}^2$. By successfully anodizing a porous aluminum surface, we combine the beneficial physical properties at both scales: the low density of the rigid porous aluminum structure and the low reflectance of the robust Anodized Aluminum Oxide (AAO) layer. This dual morphology significantly enhances the material’s optical and mechanical performance, resulting in a broadband, highly absorptive, and durable surface. The increase in hardness is linked to the generation of a porous layer through chemical etching, and the reduction in optical reflectivity in the visible and near infrared is mainly caused by the presence of nano-holes produce by anodization. The final sample demonstrates a remarkable improvement in hardness, with a twofold increase in the Vickers hardness number compared to conventional AAO layers, and a threefold increase compared to the porous aluminum layer alone. Additionally, the reflectivity of the fabricated surface is reduced by 25% relative to traditional AAO layers. These findings highlight the potential of this hybrid fabrication technique for applications requiring surfaces with superior light absorption, mechanical durability, and anti-reflective properties, such as in solar energy harvesting, optical devices, and protective coatings.