Plasmonic broadband absorber by stacking multiple metallic nanoparticle layers

High efficiency, broadband plasmonic absorbers are constructed based on a stack of alternating metallic nanoparticle layers (MNLs) and SiO₂ slabs on top of a reflective Ag substrate. Experimental results show that the stacks with thick MNLs absorb light better than those with thin MNLs when the number of MNL/SiO₂ cells (N) is small (e.g., 1 or 2), but the situation gets reversed when N is greater than 3. When the nominal thickness of MNL is as thin as 5 nm, the acquired Ag nanoparticles are so small that light penetration through all of the stacked MNLs in the proposed design is possible. Thus, an increase in N leads to a growing number of light trapping elements. Our simulation reveals that the Ag nanoparticles at different layers are hybridized to excite rich localized plasmonic resonances, resulting in multiple absorption peaks at optical frequencies and thus a broader absorption band. The broadband absorbers with an integrated absorption efficiency of 96% over the 300-1100 nm wavelength range were achieved by stacking 18 MNL/SiO₂ cells. The proposed absorbers can be used for applications in solar energy harvesting and thermal emission tailoring, due to their easy fabrication procedure and excellent optical properties.