In this work, the plasmonic coupling in silver nanosphere trimers as well as random gold nanoparticle arrays was studied. Silver nanocubes were synthesized using a polyol method, and then etched using ferric nitrate to obtain highly uniform silver nanospheres. The nanospheres assembled into dimers and trimers induced by the electrolytes in solution during synthesis, as well as from the hydrophobic effect. Individual nanosphere trimers were studied using correlated dark field scattering and scanning electron microscopy (SEM). The trimers exhibit polarization-dependent scattering spectra. In contrast to the experimental results, the theoretical studies using the T-matrix method showed that a triangular silver trimer consisted of perfectly spherical particles will have a scattering spectra that is independent of the polarization of light. Discrete dipole approximation method was used to show that slight variation in the geometry of the nanoparticle (not even obvious in SEM) will affect the plasmonic interaction, leading to polarization dependent scattering. The gold nanoparticles used in the random array were synthesized by sodium citrate reduction of HAuCl<sub>4</sub> and then grown to 120nm using a seed mediated method. They were then immobilized into a random array by self-assembly onto a silanized glass slide and the extinction was studied using localized surface plasmon resonance. In the gold nanoparticle random array, the extinction spectra blue shifts from that of both the solution and the single gold nanoparticles on glass, but it is polarization independent. Simulations using the T-matrix method show that this blue-shift is due to long-range dipole coupling. Small nanoparticle trimers show polarization dependence because of small shape differences but show polarization independence in larger random nanoparticle arrays due to long-range dipole coupling.

Plasmonic coupling in nanoparticle cluster and random arrays

251st National Meeting (2016)

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