Figures of merit of plasmon lattice resonance sensors: shape and material matters

The figure of merit (FOM) of plasmon lattice resonance (PLR) sensors based on the array of metal/Si/SiO2 nanoparticles has been investigated. We demonstrate the shape and material of metal nanoparticles have remarkable effects on the PLR and FOM. FOM is governed by full-widths at half maximum (FWHM) and sensitivity of the PLR. Three different types of PLR can be generated by changing Ag nanoparticles' shapes (pillars, cubes, spheres). One (named PLR1) is mainly originated from the coupling between Mie resonance of individual Si nanopillars and diffraction waves. PLR1 of Ag/Si/SiO2 nanoparticle arrays is limited in sensing applications due to lower intensity (for Ag pillars and Ag cubes), or smaller FOM (for Ag spheres). The other two are named PLR2. PLR2 of Ag/Si/SiO2 nanoparticle array with Ag pillars (or Ag cubes) is mainly originated from the coupling between the quadrupole resonance of individual Ag nanopillars (or Ag cubes) and diffraction waves. While PLR2 of Ag/Si/SiO2 nanoparticle array with Ag spheres is mainly originated from the coupling between dipole resonance of individual Ag nanospheres and diffraction waves. The optimal Ag nanoparticles' shape in FOM is pillar due to the smallest FWHM of PLR2 of Ag/Si/SiO2 nanoparticle array with Ag pillars. Meanwhile, a comparison of FOM between Au, Ag and Al nanopillars of fixed size is made. The optimal material of metal nanopillars to obtain a high FOM is Ag due to higher sensitivity and narrower FWHM.