A broadband absorber based on W−TiO2 ellipsoidal core-shell array structure

Abstract

In this paper, we demonstrate a new broadband perfect absorber based on an ellipsoidal core-shell array structure. The perfect absorber is formed by a core-shell nano-ellipsoid array of tungsten and titanium dioxide ($W/\text{Ti}{O}_2$). Under the TM polarization, the average absorption of the designed structure reached 97.93 % from 400 nm to 1700 nm. Besides, the average absorption rate for solar radiation can reach up to 96.64 % under AM 1.5. Physical mechanisms responsible for the high -efficiency broadband absorption are elucidated of localized surface plasmon polaritons (LSPPs) on the surface of the metallic ellipsoid, and the gap plasmon resonance(GPR) resonance at the gap between adjacent shells. Besides, the effects of geometrical sizes, like the $\text{Ti}{O}_2$ shell thickness, $W$ core radius, polarization angle, and incidence angle on the absorption line are further explored. The asymmetric elliptical spherical structure design results in more LSPPs resonance modes being excited (Such as longitudinal mode and transverse mode). The coupling of these modes enhances broadband absorption and provides more error space for the fabrication of spherical nanoparticle array structures. Furthermore, the structure shows a high thermal emissivity of 99.13 % can be achieved when the temperature reaches 1700 K. Given that $\text{Ti}{O}_2/W$ have melting points above 1700 K, and the proposed structure with $\text{Ti}{O}_2$ as shell provides low synthesis cost benefit and is used for various applications like solar energy conversion, photothermal conversion, and thermal radiators.