Multilayered metal core-shell nanostructures for inducing a large and tunable local optical field

We examine the near-field optical properties of multilayered metal core-shell sphere nanostructures by extending the Mie theory, and demonstrate that the local-field enhancement can be increased by adding new metal shells. A local intensity enhancement of more than 10⁵ times can be obtained in the cavity between the Ag core and the innermost Ag shell for proper configurations of multilayered Ag core-shell spheres. The high enhancement can be tuned from the red to the infrared region by varying the configurations of the core-shell nanostructures.