Modulation of LSPR spectra and enhanced RI-sensitivity through symmetry breaking in hollow gold nanoprism.

Optical responses of plasmonic nanostructures can be tailor-made by judiciously controlling their structural parameters. Here in this article, we describe how symmetry-breaking influences the optical properties of an anisotropic hollow nanostructure, a hollow gold nanoprism (HGN). We find that the introduction of structural asymmetry by shifting the cavity position alters the plasmon hybridization conditions, which, in turn, lifts the degeneracy of bonding plasmon modes and thereby causes mode splitting. The splitting between the nondegenerate bonding modes is directly correlated with the extent of the cavity offset. Interestingly, it is found that a reduced symmetry HGN having a cavity of any arbitrary size does not necessarily show such spectral modulation as a function of the cavity offset. Rather, there is a threshold value of (cavity diameter/edge length) ratio for observing this kind of optical behavior. Symmetry breaking not only leads to spectral modulation but also improves the refractive index (RI) sensitivity as well as the associated figure of merit of the HGN nanosensors tremendously. This comprehensive study develops a predictive understanding of the structure-specificity of the optical properties of HGNs and also suggest that sensible tailoring of the structural parameters can make HGNs as one of the most suitable candidates for RI sensing based applications.