Abstract

High-efficiency broadband plasmonic triple-layer absorbers comprised of an ultrathin Ag island layer, a ${\mathrm{SiO}}_2$ spacer, and a reflective Ag substrate are fabricated by magnetron sputtering. Experimental results reveal that surface morphologies of the fabricated Ag island film do not have regular profiles, but appear more like two or more hemi-ellipsoids randomly overlapping each other. Different from previous papers that modeled the metal island film using squared patches or regular hemi-ellipsoids, we construct the numerical model by simplifying the top metal island film as an array of overlapping hemi-ellipsoids aiming to explain the measured efficient absorption over a broad wavelength range more accurately. Through comparison, it is found that the overlapping hemi-ellipsoids can produce an additional absorption peak at the long wavelength range by the excitation of the hot-spot effect with respect to the structure with two isolated hemi-ellipsoids. Other strong absorption peaks at short wavelength ranges are also analyzed systematically. By tuning the geometry of the ellipsoids and the size of overlapping region, the absorption performance of the constructed overlapping model can be tuned. In reality, the geometries of the isolated islands are non-uniform, yielding the broad high-efficiency absorption band witnessed in experiment. Our work contributes to the design of efficient light devices for application in the area of solar energy harvesting and thermal emission tailoring.

© 2018 Optical Society of America

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