Optical Properties of 1D Plasmonic Polymers

The precise positioning and manipulation of individual nanoclusters in ordered arrangements are essential prerequisites for both comprehensive understanding and mathematical formulation to generalize the intrinsic optical characteristics for the advent of nanoscale applications. In analogy with our long-standing understanding of molecular polymers, linear chains of metallic nanostructures have been coined as plasmonic polymers, where the individual particles can be considered as the monomeric building units. The possibility of plasmonic waveguiding in these well-defined strongly coupled plasmonic nanostructures has motivated their investigation as prototypical model systems to fulfill the modern demand of applications in photonics miniaturized at the nanoscale dimensions. 1D chain-like assemblies of nanostructures, because of their high symmetry, represent particular spatial arrangements for propagating surface plasmon polaritons that can venture directed energy transfer along the chain and to unravel short- and long-range electromagnetic coupling mechanisms in these oriented assemblies. The optical properties of these plasmonic polymers are dependent upon the structural characteristics, such as the aggregation number, interparticle distances, and mutual orientations that explicitly correlate with the degree of polymerization, bond lengths, and bond angles, respectively, in these lattice architectures. Moreover, the morphological characteristics, such as size, and geometry of the individual building blocks, are of paramount significance to the critical condensation of the intriguing optical features in these polymeric configurations. The cumulative effect of all these intrinsic physical observables associated with the polymeric configurations can reckon the complete story towards the observed plasmonic properties. As to the first initiative to distill this complex relationship, a theoretical formulation has been devised in simple intuitive terminologies to correlate the chain length dependence on the plasmonic characteristics and electric field distribution patterns in 1D aggregation of size-selective gold nanostructures. The complementarity of theoretical, experimental, and numerical simulation approaches has been adopted in bridging the interrelation between the associated physical parameters and optical characteristics of the periodic assemblies with varying chain lengths comprised of size-selective gold nanoparticles. The unique ability of plasmonic waveguiding and coherent exchange of near electric fields along these 1D chain-like assemblies can endow newer perspectives towards their potential applications in light-trapping in photovoltaic devices, nanoscale photonics, optical circuitry, chemical and biological sensing, and surface enhanced spectroscopies.