| Since the concept of plasmonics perfect absorber was first proposed,the development of perfect absorbers has evolved from single-band absorption to multi-band absorption,to broadband absorption,and to narrow-band absorption.In recent years,in the high-frequency bands where stronger solar radiation,especially in the near-infrared,visible and ultraviolet region,achieving multi-band absorption for high-sensitivity sensing or broadband absorption for solar cell applications have become a research hotspot.In this text,we propose an ultraviolet broadband plasmonic absorber with dual narrow bands located separately in the visible and near-infrared regions.The absorption efficiency is greater than 99.9% at wavelengths of 660 nm and 919 nm(visible and near-infrared),respectively,under normal incidence.In the ultraviolet region from 240 to 500 nm,the absorption efficiency can be achieved over 90%.The geometric symmetry of ring square makes the perfect absorber polarization-independent,and insensitive to large incident angle.On the other hand,we propose a broadband perfect absorber structure based on insulator-metal-insulator-metal four-layer structure,theoretically designing and numerically verifying three broadband perfect absorbers working in the ultraviolet,visible and near-infrared regions: Firstly,full visible light broadband perfect absorber consists of silica-titanium nitride-silica-titanium nitride four-layer structure,which has an ultra-thin thickness of 325 nm.This broadband absorber can achieve continuous perfect absorption from wavelength 400 to 800 nm,with an average absorption of 99.52% under normal incidence.And absorber obtained 99.98% maximum absorption rate at wavelength 620 nm and 97.18% minimum absorption rate at 400 nm.The multiple integration of propagating surface plasmon resonance,localized surface plasmon resonance,and Fabry-Perot resonance generates the broadband perfect absorption.Secondly,visible to near-infrared broadband perfect absorber with an elliptical titanium nanodisk array based on a silica-titanium-silica-titanium four-layer structure,it can achieve ultra-broadband absorption above 90% from a visible 550 nm wavelength to a near-infrared 2200 nm wavelength continuously.In particular,a continuous 712 nm broadband perfect absorption of up to 99% is achieved from wavelengths from 1013 to 1725 nm.The air mass 1.5 solar simulation from a finite-difference time domain(FDTD)demonstrates that this absorber can provide an average absorption rate of 93.26% from wavelength 295 to 2500 nm,which can absorb solar radiation efficiently on the earth.Thirdly,ultraviolet to near-infrared broadband perfect absorber has 280 nm ultra-thin thickness,and the combination of refractory metal titanium nitride and high-melting-point insulator silica gives our absorber strong thermal stability.The novel titanium nitride ring-square array layer combines the absorption of different wavelength bands so that the absorber can achieve a continuous absorption of more than 90% from wavelength 200 to 1200 nm.Calculated average absorption rate reaches 94.85%,which 99.40% maximum absorption at wavelength 270 nm and 90.30% minimum absorption at 390 nm.In addition,polarization independence under normal incidence and large incident angle insensitivity under oblique incidence,making our perfect absorber more advantageous in applications such as solar energy collection,photothermal conversion,and invisibility cloak.Finally,to summarize the full text and clear the goal,the future work will focus on the design of multi-band perfect absorption device combining wide and narrow band,and explore the full solar spectrum broadband perfect absorber. |
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