Size and Shape Dependence of Localized Surface Plasmon Resonances

Size and Shape Dependence of Localized Surface Plasmon Resonances 

Dipartimento di Fisica, Universita degli Studi di Pavia, 

National Nanotechnology Laboratory, Istituto Nanoscienze-CNR, ViaArnesano 16,1-73100 Lecce, Italy stefania.dagostino unipv.it 

In this chapter the influence of the structural parameters on the optical behavior of silver nanoparticles is anal3fzed. The absorption and scattering spectra are obtained for particles with different size and shape in the framework of the discrete dipole approximation. Radially symmetric nanoparticles, as well as finite-number faces nanoparticles or multi-tips objects are investigated under the excitation of uniform fields impacting with different poiarizations and propagation directions. The optical responses can be assigned to the excitation of iocalized surface plasmon resonances of different order. The presented results can be used to interpret experimental measurements and/or to develop new high-performance substrates for molecular plasmonics applications. 

Plasmonic resonances in metallic nanoparticles can be controlled by optimizing the nanoparticle topology, dimensions, and composition [1-3]. 

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SERS activity, which mainly arises from localized surface plasmon resonance, depends critically on the optical properties, size, shape, and inter-particle space of nanostructures. 

The localized surface plasmon resonance of individual plasmonic nanoparticles depends heavily on the size and shape of each nanoparticle. For instance, the wavelength of the dipolar surface plasmon red shifts with the increase of particle size. However, for much larger nanoparticles new bands for some multipolar modes will appear in the short-wavelength range, while the dipolar band at long-wavelength will be damped. Typically, the size of Au or Ag nanoparticles synthesized for SERS should be less than 150 nm, and larger than 20 nm. 

LSPR frequency is dependent on the size, shape, material properties and the effect of the dielectric medium around the nanoparticles. They determine the position and width of the plasmon resonance. Due to the confinement of the SP to the metal nanoparticle, excitation of surface plasmons can result in selective photon absorption, scattering and a large enhancement of the local electric field in the close vicinity of the metal nanoparticles. Hence, varying these parameters offers the tunable resonance position to engineer plasmonic structures to target weakly absorbing regimes of various types of solar cells [5]. 

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