ABSTRACT
Localized Surface Plasmon Resonance (LSPR) mediated electromagnetic field enhancement play a vital role in enhancing the performance of bio-molecular sensors, photovoltaic cells and Raman spectroscopy (e.g., in SERS) etc., to name only a few. It is now well established that the field amplification factor (mode squared field) ~106 for spherical shaped plasmonic nanoparticle dimers is significantly higher than the amplification factor of a monomer which is ~103. In this work, a theoretical and semi-analytical approach based on multipole spectral expansion is used to investigate the electric field enhancement in the gap region of spherical nanoparticle dimers of Al, Rh, Ag, and Au. The dimer exhibit rich spectra compared to its isolated counterpart. For example, in contrast to a monomer, the dimer spectra consists of multiple resonant peaks which can be fine tuned by varying particle size and/or inter-particle separation. Moreover, the enhancement in dimer is several orders higher than that in monomers. Rich spectral features in dimer spectra arise from the interaction between particle plasmons of constituent NPs and their hybridization, which results in the splitting of plasmonic energy levels. We carry out, systematic investigation of these systems to quantify the effect of particle size, interparticle separation and metal type (Al, Ag, Au, Rh) on electric field enhancement.
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