Effects of Dielectric Spacer on Absorbance Characteristics of a Dual-Band Nanoaperture Based Perfect Absorber

Abstract

In this study, a novel perfect absorber (PA) array based on H-shaped nanoapertures for bio-sensing applications in infrared regime is presented. Proposed PA array has a dual-band spectral response, and the locations of these resonances can be adjusted by varying the geometrical dimensions and layer thicknesses of the structure. Nearly unity absorbance is obtained from the PA array for both resonances. The structure design is based on the near field plasmon coupling between the gold film layer and the top nanoaperture array. In this context, the dielectric spacer layer is used to support this plasmon coupling and the gold film on the silicon substrate is also utilized to eliminate the transmittance through the structure. Different dielectric spacers (MgF2, SiO2, and Al2O3) are used to investigate the effects of dielectric spacer on the absorbance characteristics of proposed PA array. High field enhancement is achieved by the interaction of the sharp corners of nanoapertures. The near field enhancements are more than 1500 times at the first resonance frequency, more than 1000 times at the second resonance frequency which is highly desirable for the infrared bio-sensing applications. Due to the high near-field enhancement and nearly unity absorbance, the proposed dual-band PA array with adjustable spectral responses can be useful for bio-sensing applications in infrared regime.