Template-Stripped Truncated Nanoscale Pyramid Arrays for Refractive Index Sensing

Subwavelength optical confinement in nanophotonics is promising for enhancing light-matter interactions, nanolasering, biosensing, etc. However, it is nontrivial to achieve a high-performance refractive index (RI) sensor because of the high internal optical loss and radiative damping in the metallic nanostructures. Here, we theoretically proposed and experimentally demonstrated truncated nanoscale pyramid arrays to construct high-performance RI sensors based on the template-stripped approach. The root-mean-square (RMS) surface roughness reached a low value of 0.31 nm to reduce its surface scattering. Arising from the coupling of Fabry–Pérot (FP) and surface plasmon polariton (SPP), an experimental resonance with a linewidth as low as 14 nm and a sensitivity of 829 nm/RIU is demonstrated. By increasing the size of truncated nanopyramids, a figure of merit (FOM) of 80.3 and linewidth down to 9 nm in refractive index sensing are also achieved. A truncated-pyramid-based RI sensor presents superiority between sensitivity and/or FOM experimentally compared with many other RI sensors. The results suggest that our proposed design is a promising platform for the applications of biomedical sensing, optical components, environmental monitoring, and so on.