Nanoscale noble noble metal particles are well known for their ability to sustain resonoant electrón plasma oscillations, knowm as particle plasmon. This phenomena give rise to a spectrally selective light absorption and scattering ant to a considerable enhancement of the local electromagnetic (near field) with respect to the excited light field. The resonance wavelength of a particle plasmon for a given metal is strongly dependent of the size and shape of the particle as well as on the surrounding medium. Thus, tailoring the particle geometry allows a direct control of the particle plasmon properties.
In this work, we have performed a systematic theoretical study of the optical properties *absorption, scattering and extinction( of silver and gold nanorods as a function of size, shape and dielectric environment. These simulations are of particular relevance to recent experiments on lithographically and chemically designed metal nanoparticles.
The electromagnetic calculations were performed using the Discrete Dipolo Aproximation (DDA) which relies on as real-space discretization of the object under investigation.
In contrast to spheres, where the extinction bands of the respective multipolar palsmons resonances overlap considerably to form a broad spectrum, spectrally well defined bands corresponding to plasmons of different order were found. The number and separation of these resonances is highly dependent on particle length, transversal section and dielectric environment. These results are in agreement with recent experiments with silver and gold nanorods.
