Plasmon field enhancement in silver core-protruded silicon shell nanocylinder illuminated with light at 633 nm.

We show, to the best of our knowledge, the first simulation result of the strong plasmonic field coupling and enhancement at the Ag/Si interface of a silver core/protruded silicon shell nanocylinder by using the finite-element method. The strong plasmon field, with a slow effective phase velocity accumulated at the Ag/Si interface, which results from the large effective index of the surface plasmon due to the nearly identical real parts with opposite signs of the permittivities of silver and silicon at 633 nm, is analyzed. When the silicon shell has shallow protrusions of proper periodicity to meet the phase matching condition between the incident light and the surface plasmon wave at the Ag/Si interface, a higher scattered electric field and a higher sensitivity to the refractive index change of the surrounding medium can be achieved. Furthermore, a feasible implementation of the core-shell nanocylinder design concept is studied and discussed.