Tunable Palladium Nanopores for Broadband Optical Absorber Coatings

Nanoporous palladium (np-Pd) is of interest for broadband optical absorber coatings, photothermal conversion, and plasmon-assisted catalysis because it combines metallic conductivity, high surface area, and hydrogen uptake capability within a single material system. However, to achieve high optical absorptivity, other plasmonically active materials are often employed to attain the necessary optical absorption. Here we demonstrate a simple, scalable route to tunable np-Pd thin films formed by chemical dealloying of co-sputtered Pd−Cu alloys. Composition- and angle-resolved absorption reveal broadband absorptance exceeding 85% between 450 nm and 800 nm. Effective-medium modeling based on Maxwell−Garnett theory accurately links the measured porosity to an effective dielectric function, while finite-difference time-domain simulations suggest morphology-driven plasmonic hot spots at Pd ligaments and junctions, with maximum local near-field intensity enhancements, |E/E0|2, of order 102 for the idealized simulated surfaces within the visible-to-near-infrared spectral range. This composition-controlled dealloying route provides a scalable strategy for np-Pd broadband absorber coatings, with potential extensions to photothermal conversion, plasmon-assisted catalysis, and hydrogen-related surface processes.