Environmental Symmetry Breaking Promotes Plasmon Mode Splitting in Gold Nanotriangles

We report a single particle investigation of the polarized scattering spectra of individual Au nanotriangles (NTs) of the truncated bifrustrum type. We unexpectedly observed a wide diversity in the scattering spectra from a population of NTs with low shape polydispersity. Correlation of the optical measurements with electron microscopy revealed that the different optical responses were not due to distinct NT shapes. Rather, finite element simulations revealed that distinct polarized spectra originated from minute changes in the inclination of the NTs on the substrate. NT inclination resulted in asymmetric image charge formation in the substrate, thus, breaking the degeneracy of the modes supported by the NTs. The degeneracy of the NT modes was extremely sensitive to such symmetry breaking, with inclination angles as small as 2 degrees, producing clearly resolved, nondegenerate, and orthogonally polarized plasmon modes.