Design and numerical analysis of a trapezoidal multilayer nano-wedge stack for dual-functional ultra-broadband absorption

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Chinese explanation / 中文解读

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Original abstract

Introduction Achieving ultra-broadband, near-unity light absorption across both solar and thermal spectral ranges remains a critical challenge for next-generation energy harvesting and high-temperature thermal emission applications. Conventional absorber designs are limited by narrow spectral bandwidth, polarization sensitivity, and angular dependence, motivating the development of advanced nanostructured architectures capable of simultaneous dual-functional performance. Methods This study presents the computational design and rigorous numerical analysis of an asymmetrically-cascaded trapezoidal-profile multilayer nano-wedge absorber comprising tungsten (W), hafnium oxide (HfO 2 ), and zirconium nitride (ZrN) thin films. The architecture features progressively tapered W/HfO 2 bilayer units arranged in a unidirectional asymmetric cascade atop an optically opaque ZrN ground layer, forming a staircase-like ramp with non-centrosymmetric lateral periodicity. Systematic geometric parameter studies, material substitution screening, and structural configuration comparisons were conducted to identify optimal design parameters across the 300–4500 nm spectral range. Results The optimized device achieves a spectrally averaged absorptivity of 97.2%, sustaining values above 90% over an ultra-broadband interval of 4200 nm. Evaluation under the AM1.5G solar spectrum yields a solar spectral conversion efficiency of 95.8%, corresponding to minimal optical losses of 4.2%. In Planckian thermal emission mode, near-ideal emissivities of 98.1% at 1000 K and 97.9% at 2000 K are observed, approaching the theoretical blackbody limit. Three distinct absorptivity resonance peaks at λ 1 = 390 nm, λ 2 = 920 nm, and λ 3 = 3150 nm are identified, attributed respectively to a magnetic dipole resonance (MDR) in the top W nano-wedge layer, a guided cavity resonance (GCR) within W/HfO 2 /W Fabry–Pérot-type nanocavities, and a low-frequency inter-gap plasmonic resonance (IGPR) in deep-subwavelength lateral nanogaps. The device maintains absorptivity above 97% under TM-polarized incidence up to 40° and exhibits improved TE-polarized absorption at oblique angles. Discussion W is identified as the optimal metallic constituent for maximizing dual-functional performance through material substitution screening. The complementary interplay of three distinct electromagnetic confinement mechanisms across the ultraviolet, near-infrared, and mid-infrared regions underpins the exceptional broadband response. The robust angular and polarization performance, combined with near-blackbody thermal emissivity at elevated temperatures, establishes the asymmetric-cascade nano-wedge design as a highly promising platform for solar energy harvesting and high-temperature selective thermal emission applications.

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