Plasmonic Broadband And Efficient Electromagnetic Absorber Based On The Flat And Structured Substrates

Electromagnetic wave absorbers have drawn increasing research interests recently due to their wide applications in many areas,such as solar-energy harvesting,thermal emitters and so on.Up to date,a series of absorbers based on different materials and configurations have been proposed and demonstrated.Narrowband absorbers can be used in areas like selective thermal emitters and biosensing.In other applications like solar energy harvesting,sea water desalination and camouflage,broadband/multiband absorbers which can absorb light efficiently over a broadband wavelength range or multiple bands are desirable.However,most of the broadband/multiband absorbers require expensive fabrication techniques,such as electron beam lithography or focused ion beam milling,which are time-consuming and unsuitable for large area fabrications.From this context,broadband absorbers made by simple fabrication techniques are highly desirable.In this paper,plasmonic broadband absorbers made by sputtering based on the modified metal-insulator-metal?MIM?configuration are fabricated and investigated on the flat and structured substrates,respectively.Firstly,we changed the top metal film in the MIM structure to metal nanoparticles with random shapes and sizes,which were formed automatically during deposition.The metal particles on the top layer will excite plasma resonances at different wavelengths which can broaden the absorption bandwidth of the absorber.The optical performances of samples with different metal nanoparticles layer thicknesses?tm?and different dielectric layer thicknesses?td?on the flat substrate with the smooth and rough surface were studied.While tm?td?kept unchanged,Aint increased first and then decreased with the increase of td?tm?.Aint of 89.8% and 90.4% over the 300 1000 nm wavelength range on the two kinds of substrate were obtained with tm = 5.4 nm and td = 90 nm.It is worth mentioning that,the sample deposited directly on polished Al substrates had an Aint of 91.2% over the 300 1000 nm wavelength range with tm = 5.4 nm and td = 90 nm.Secondly,the MIM absorbers on the structured substrates were fabricated and investigated.We demonstrated a flexible,wide-angle,broadband and high efficiency absorber with Aint of 95.6% over the 300 1100 nm wavelength range on the flexible substrate with moth-eye pattern,when the td and the tm is 96 nm and 5.4 nm,respectively.The results indicated that the broadband absorber was insensitive to the thickness of the SiO₂ layer.When td is 0 nm,t Aint is 84.3% over the wavelength range from 300 nm to 1100 nm.Especially,the absorber is insensitive to the incident angle,Aint can maintain to 90.2% when the incident angle is as large as 600.Moreover,the device shown excellent flexible properties,when the bending cycles increase to 10000,Aint maintains 98.7% of its original value.Therefore,the designed absorber has potential applications in the fields of buliding-integrated photovaltaics and protable power sources.We also studied the absorption performances of the absorbers with different thicknesses of the bottom metal on AAO substrates.With the increase of the bottom metal,the absorption efficiencies decreases in the wavelength range from 650 nm to 1100 nm.Finally,the conclusion is presented and outlook is put forward.