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

The research on broadband electromagnetic absorbers has become one of the most popular research topics in the electromagnetic field,and their application fields are extensive,such as the solar photovoltaic industry,electromagnetic protection equipment,stealth fighter,etc.In recent years,metal-insulator-metal?MIM?electromagnetic absorbers have been attracting research attentions for their unique simplicity and ease of fabrication.In this thesis,a multi-band absorber is prepared by periodically stacking thin metal layers and dielectric slabs on a flat substrate.On the other hand,a high-efficiency,broadband absorber is obtained by preparing a single-cycle metal/medium/metal structure on a textured substrate.First,multiband absorbers comprised of one dimensional periodic Ag metallic thin layer and MoO₃/Si O₂ dielectric layer on a reflective Ag thick layer were fabricated by thermal evaporation and magnetron sputtering methods.Experimental results show that with the number of unit cell?N?increasing,the number of the absorption peaks increases accordingly and precisely equals N.For our fabricated devices with 14 nm thick Ag layer,2 nm thick MoO₃ layer,and 135 nm thick SiO₂ layer,the integrated absorption efficiency over the wavelength range from 400 nm to 900 nm increases from 29.4%when N=1 to 57.2%when N=6,the trend of which is consistent with the calculation results.Moreover,measurements show that the absorption peaks are insensitive to the incident angles and polarizations.We also fabricated the multilayer absorbers on flexible polyethylene terephthalate substrates,which maintained their original absorption performances after bending for 1000 times.On the other hand,single-period metal/insulator/metal absorbers were fabricated on a structured substrate which was self-assembled with the PS microspheres.Three dielectric layers were used in the absorbers,i.e.,SiO₂film,MoO₃ film,and PVP film.They all exhibited broadband absorption in the wavelength range of 400-900 nm.Each layer of the absorber fabricated on the structured substrate had a structured profile,which forms various photonic resonances at different wavelengths,resulting in efficient light harvesting over a broadband wavelength range.Finally,broadband and high efficiency absorbers fabricated on AAO template show an absorption efficiency close to 99%and the sample color appears to be black.The main mechanism of its absorption is that the metal particles attached in the pores of the double-pass AAO template generate localized surface plasmonic effect,which has a strong local effect on light and good absorption efficiency.Finally,we summarize this thesis,and present the outlook of the further investigation.