Ultra-sensitive narrow-band plasmonic perfect absorber for sensing applications

Plasmonic nanostructure-based sensors have a broad range of applications in food assessment, hazardous gas monitoring, medical diagnosis, and vapor sensing. However, it is still challenging to establish a high performance plasmonic sensing platform that simultaneously provides high refractive index sensitivity and high figure of merit values. Based on simulations using the finite element method, we engineered an ultra-sensitive all-metal plasmonic perfect absorber (a-MPPA) for sensing applications. The proposed a-MPPA structure is based on closely spaced silver (Ag) nanocones over an Ag thin film and it exhibits ultra-sharp spectral absorption with robust hot spots of electric and magnetic fields. The high optical absorption and localized giant field enhancement depend on the structural configuration of the platform. We observed that the absorbance of the optimized structure exceeded 99%, with an ultra-narrow plasmonic peak (4.3 nm), thereby suggesting that the proposed nanostructure is a good candidate for sensing applications. The sensing performance of the a-MPPA platform was outstanding, with bulk sensitivity of 1006 nm/RIU, large figure of merit value of 233.9 RIU-1, and high quality factor of 233.4. Theoretical analyses based on Campbell's model indicated that the a-MPPA platform is suitable for molecular detection, with a detection range extending to 50 nm. The proposed narrow-band perfect absorption plasmonic nanostructure has great potential for applications in sensing.