Nanoscale coupling effects on single particle microscopy

We present theoretical studies and experimental results on the optical properties of gold, octahedra-shaped nanoparticles. We show that the optical spectrum varies quite dramatically as two nanoparticles are brought into close proximity. AFM images and optical spectra have been obtained for nanooctahedra dimers in uncoupled and strongly coupled configurations. The former displays a single peak in the optical spectrum, while the latter shows an additional peak at longer wavelengths. Calculations indicate that the additional spectral feature originates from a strongly coupled plasmon state that oscillates along the extended axis of the dimer. We investigate theoretically the distances over which the dimers couple and find these results to be particularly orientation dependent. The anisotropic particle shape and sharp apices contribute significantly to the orientational dependence of the interparticle couplings.