All the plasmonic solid nanoparticles, single Ag or Au nanocubes are known to be plasmonic nanoparticles with strong plasmonic fields, which are concentrated around their corners. However, when two Ag or Au nanoparticles are in close proximity to each other and the incident exciting light is polarized parallel to the interparticle axis, strong electromagnetic fields (hot spots) are formed between the monomers . The hot spots are generated due to the strong coupling of the excited oscillating dipoles on the facing facets as well as at the corners of the two nanoparticles of the dimer. The relative orientation of the nanoparticles and the size of the gap between them determine the near field coupling behavior of the two monomers in the dimer. This distance is dependent on the size of the nanoparticles as well as the relative orientation of the two nanoparticles. The contribution from the coupling with the higher order multipoles (e.g. quadrupole) is responsible for the breakdown of the universal exponential rule. In order to examine the sensitivity factor of the face to face (FF) oriented Ag NCs dimer, the localized surface plasmon resonance (LSPR) maximum is determined as a function of the refractive index of the surrounding medium for the two prominent plasmonic bands in the extinction spectrum. It was found that the LSPR bands that have higher sensitivity factors correspond to those having large electromagnetic field distribution and not necessary the ones with the highest extinction. Additionally, we found that the LSPR spectrum and field distribution around the FF oriented Ag NC dimer are sensitive to the substrate refractive index and excitation order of the incident light as well. A substrate of high refractive index showed significant change in the extinction spectra and the field enhancement due to the multipole modes of the Ag NC dimer. Studies on the effects of the substrate location with respect to the propagation direction of the exciting light revealed that If the incident light passes through the strong absorbing substrate first, the plasmonic light produced will be much weaker as the intensity of exciting radiation will be greatly reduced compared with that when the exciting light passes through the FF oriented Ag NC dimer faces first.<br/>

Dependence of the plasmonic properties of two silver nanocubes  on their separation, relative orientation, refractive index of the substrate and propagation direction of the exciting light

253rd National Meeting (2017)

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