Abstract
We fabricated and experimentally studied Au nano-foams and Al2O3 scaffolds filled with Au nanoparticles (NPs). We found that while the reflectance spectra of Au nano-foams depended very little on the 8-10 nm Al2O3 ALD coating, the spectra were highly sensitive to annealing, which increased the sizes of voids and ligaments from 50-100 nm to ∼300 nm. The effective dielectric permittivities of the Au nano-foams and Al2O3 scaffolds with Au NPs were extremely high, ∼50. At the same time, Au nano-foams covered with a dielectric (MgF2) featured bright structural colors, calling for the model, which extends beyond the effective medium approximation.
Highlights
Advanced photonics applications require materials with extreme responses to electromagnetic waves in the optical range of the spectrum
The large-scale exploration of such unique materials has started nearly two decades ago, and a remarkable progress has been made in the development of metamaterials – engineered composite materials comprised of subwavelength “meta-atoms” with rationally designed shapes, compositions, sizes and mutual orientations
Most of metamaterials are fabricated in a clean room environment using the “top down” approach, which limits their lateral dimensions to the ∼100 μm scale
Summary
Advanced photonics applications require materials with extreme responses to electromagnetic waves in the optical range of the spectrum. (Received 19 March 2018; accepted 27 August 2018; published online 4 September 2018)
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