LSP modes of Ag nanocube and dimer studied by DDA simulation

Optical properties of symmetry-breaking tetrahedral nanoparticles

Spectrally rich but geometrically simple plasmonic metallic nanoparticles are highly favored in nanophotonics. However, they remain elusive owing to the symmetry-induced mode degeneracy and interband transition-induced plasmonic damping. Hence, most nanoparticles exhibit a single major extinction peak originating from the lowest-order dipole resonance. In this study, we uncover that even a simple tetrahedral nanoparticle supports rich spectral features due to symmetry breaking. This discovery runs counter to the reported gold tetrahedral nanoparticles, where only a single extinction peak was observed. We find that, in the case of a tetrahedral nanoparticle, the plasmonic quadrupole vertex mode becomes a bright mode and hybridizes with the dipole vertex mode, which splits the extinction peak and contributes to spectral diversity and tunability. The peak splitting is also found to be sensitively dependent on the roundness of vertices and edges. Furthermore, the tetrahedral depolarization factors are determined using the previously generalized absorption coefficient. We envision that this work will not only help fill the gap in understanding the optical properties enriched by symmetry breaking but also guide the superior probe design by combining spectral tunability with geometric simplicity of the nanoparticle.

Bulk scale fabrication of sodium tungsten bronze nanoparticles for applications in plasmonics

In order to advance plasmon-based technologies, new materials with low damping losses and high chemical stability are needed. In this letter, we report the bulk scale fabrication of sodium tungsten bronze (Na _x WO₃) nanoparticles with high Na content (x ≤ 0.83) using a furnace-assisted method. Phase purity and morphology is confirmed with x-ray diffraction and scanning electron microscopy. Plasmon responses are characterized using spectrophotometry and spatially-resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope. Experimental EELS maps of individual nanoparticles show the excitation of distinct plasmon resonances at visible and near-infrared (NIR) frequencies, and these observations are supported by boundary element method simulations. Na _x WO₃ is a promising alternative material for plasmonics due to its strong plasmon resonances when compared to Au, its simple nanofabrication, and low cost. In particular, their high NIR extinction makes these materials ideal for applications in solar control window coatings or plasmonic photocatalysis.