Optical effects near metal nanostructures: towards surface-enhanced spectroscopy

Abstract

The trapping of light at the surfaces of nanomaterials gives rise to regions of enhanced electric fields around the nanostructures, leading to enormous optical crosssections for molecules in the vicinity. The finite difference time domain method has been used to calculate the near-field as well as the far-field optical properties of spherical Au nanoparticles and Au nanorods as a function of their size. Au nanoparticles are found to give rise to about an order of magnitude enhancement in the electric field of the incident light. For Au nanorods,we find three orders of magnitude enhancement under resonant conditions for the longitudinal polarization of the incident light. This aspect has been utilized for the preferential functionalization of oppositely charged Au nanoparticles onto the edges of Au nanorods. Plasmon resonances of Au nanorods couple when they are in proximity and the junctions between the nanorods are regions of enhanced electric fields