Self-assembled metamaterial perfect absorbers at visible wavelengths using core–shell Au@SiO2 meta-atoms

Abstract

Light absorbers have widespread applications in plasmonic sensing, optical imaging, solar energy harvesting and photovoltaics. In this paper, a new class of metamaterial perfect absorbers (MPAs) is presented: core–shell Au@SiO₂ meta-atoms randomly arranged onto an aluminum nanofilm that is capable of the near-perfect absorption of visible light over a wide spectral wavelength region. The MPAs were fabricated by a facile bottom-up self-assembly technique at the air–liquid interface. Interestingly, core–shell Au@SiO₂ plasmonic nanoparticles (NPs) were designed as the meta-atoms and a matched synergistic electrostatic and capillary self-assembly strategy was proposed. Optical characterization showed that the well-designed MPA with four layers of Au@SiO₂ meta-atoms exhibited a particular absorption behavior at visible frequencies: two near-perfect absorption peaks (absorptance both above 99%) were recorded near λ = 537 nm and λ = 575 nm with TE- and TM-polarized light, respectively, at different incident angles. Moreover, under ∼45° incidence, the TE-polarized light absorption (average absorptivity of more than 90%) of the MPA ranged from 506 to 580 nm, suggesting that the MPA achieved a polarization-dependent broadband response. It has been demonstrated that the exotic absorbing properties of our designed MPAs were due to the effective Mie resonances (localized and coupled Mie resonances) from adjacent Au@SiO₂ meta-atoms and the positive interferometric enhancement from the SiO₂ dielectric shells. Besides, the proper self-assembled layer (i.e. 4) of Au@SiO₂ meta-atoms and the suitable light incidence angle (i.e. 45 degrees) were critical for the desired resonance absorption behaviors.