Tunable optical antennas based on metallic nanoshells with nanoknobs.

We investigate optical properties of a new complex plasmonic nanostructure, which consists of a spherical metallic nanoshell and a small metallic nanoparticle ("nanoknob") situated on its surface. The plasmon resonance wavelength of the entire structure is guided by the geometrical and material properties of the nanoshell whereas the electromagnetic field of the incident light is localized and enhanced near the "nanoknob". The idea is supported with electromagnetic modeling and near-field optical microscopy imaging. In addition, we proposed and demonstrated a new method of nanoparticle precise manipulation under electron beam, which could be used in fabrication of such plasmonic structures and other nanosized elements.