Exploiting extreme coupling to realize a metamaterial perfect absorber

An optical metamaterial, operating in between the MID/IR and the visible domain, which uses the effect of extreme coupling between closely spaced nanostructured gold metal plates and a planar gold substrate was realized by means of electron beam lithography and lift-off technique. This regime is only accessible by using an ultrathin oxide layer between metal plates and substrate, where the oxide layerisrealized by atomic layer deposition here. The involved fabrication is discussed in detail. The metamaterial shows the predicted effect of perfect absorption with multiple resonances in the spectral range from 100 THz to 600 THz. The plasmonic based resonance frequencies are very sensitive to the plate size of the grating and the spacer thickness.

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► A perfect absorber metamaterial for the spectral range of 100–600 THz was realized.
► Absorption is based on strong coupling between a 2D gold grating and a gold substrate.
► Grating and gold substrate are closely separated by an ultrathin oxide layer.
► Plasmonic resonance frequencies are very sensitive to dot size and spacer thickness.