Metal nanoparticles (MNPs) have been intensively studied within the past decade due to their unique properties which find applications in a broad range of different fields, ranging from chemistry to physics, from biology to materials science and medicine. The optical behaviour of MNPs is mainly due to the fact that they support localized surface plasmon resonances (LSPRs), which are excited when an incident electromagnetic radiation creates collective coherent oscillations of the particle free electrons. Such plasmon excitations result in a large enhancement of the electromagnetic field around the nanoparticle, yielding both a strong absorption and scattering of light by the nanoparticle at the plasmon resonance. We investigate the near-field and far-field optical behaviour of gold nanoparticles through a computational approach based on the multipole expansion of the electromagnetic field and the Transition matrix method. We model the nanoparticles as isolated spheres or dimers, considering both the case of homogeneous composition and the case of nano-shell structures. Upon optical excitation, the maximum near-field enhancements in metal nanoparticles occur at lower energies than the maximum of the corresponding far-field quantities. This effect has been much debated in the literature, but the physical explanation of this apparently universal behaviour of metal particles is still controversial. The understanding of the red shift effect appears particularly important for the optimization of surface enhanced spectroscopies. In this presentation we will investigate the dependence of the red shift effect on the nanoparticle size and shape, starting our investigation with a homogeneous gold nanosphere and successively extending the description to the case of nanoshell particles and dimers. We will also discuss the physical origin of this effect in terms of the radial field components, following the inspiring work by Messinger et al (1981). Finally we will attempt to draw a comparison with data obtained from Surface Enhanced Raman Scattering (SERS) experiments on gold nanoparticle samples deposited on a substrate.
Near-field and far-field optical behaviour of gold nanostructures in the T-matrix approach
2013
Abstract
Metal nanoparticles (MNPs) have been intensively studied within the past decade due to their unique properties which find applications in a broad range of different fields, ranging from chemistry to physics, from biology to materials science and medicine. The optical behaviour of MNPs is mainly due to the fact that they support localized surface plasmon resonances (LSPRs), which are excited when an incident electromagnetic radiation creates collective coherent oscillations of the particle free electrons. Such plasmon excitations result in a large enhancement of the electromagnetic field around the nanoparticle, yielding both a strong absorption and scattering of light by the nanoparticle at the plasmon resonance. We investigate the near-field and far-field optical behaviour of gold nanoparticles through a computational approach based on the multipole expansion of the electromagnetic field and the Transition matrix method. We model the nanoparticles as isolated spheres or dimers, considering both the case of homogeneous composition and the case of nano-shell structures. Upon optical excitation, the maximum near-field enhancements in metal nanoparticles occur at lower energies than the maximum of the corresponding far-field quantities. This effect has been much debated in the literature, but the physical explanation of this apparently universal behaviour of metal particles is still controversial. The understanding of the red shift effect appears particularly important for the optimization of surface enhanced spectroscopies. In this presentation we will investigate the dependence of the red shift effect on the nanoparticle size and shape, starting our investigation with a homogeneous gold nanosphere and successively extending the description to the case of nanoshell particles and dimers. We will also discuss the physical origin of this effect in terms of the radial field components, following the inspiring work by Messinger et al (1981). Finally we will attempt to draw a comparison with data obtained from Surface Enhanced Raman Scattering (SERS) experiments on gold nanoparticle samples deposited on a substrate.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
