Plasmonic hybridization generation in self-aligned disk/hole nanocavities for multi-resonance sensing.

Plasmonic nanostructures have proven an extensive practical prospect in ultra-sensitive label-free biomolecule sensing due to their nanoscale localization and large near-field enhancement. Here, we demonstrate a photonic plasmonic hybridization in the self-aligned disk/hole nanocavity array under two specific cases of nanogap and nanooverlap achieved by adjusting pillar height embedded into hole. The proposed disk/hole arrays in above two cases exhibit three hybridized modes with extremely high absorption, mainly arising from the in-phase (bonding) and out-of-phase (antibonding) coupling of dipolar modes of their parent disk and hole. Surprisingly, when the nanogap feature of the disk/hole array is transformed to the nanooverlap, crossing the quantum effect region, the bonding mode in the disk/hole array has an enormous transition in the resonant frequency. In comparison with the counterpart in the nanogap structure, the bonding mode in the nanooverlap structure supports strongest near-field localization (i.e., the decay length down to merely 3.8 nm), although charge transfer channel provided by the geometry connect between disk and hole quenches partial field enhancement. Furthermore, we systematically investigate the sensing performances of multiple hybridized modes in above two cases by considering two crucial evaluating parameters, bulk refractive index sensitivity and surface sensitivity. It is demonstrated that, in the nanogap structure, the bonding mode possesses both high bulk refractive index sensitivity and surface sensitivity. Dissimilarly, for the nanooverlap structure, the bonding and antibonding modes show different surface sensitivities in different regions away from the surface, which can be used to monitoring different bio-molecular sizes and achieve the most optimum sensitivity. Due to its unique sensing features, this disk/hole array mechanism is very valuable and promising for developing of high sensitivity sensing platform.