Metallic Nanoshells with Sub-10 nm Thickness and Their Performance as Surface-Enhanced Spectroscopy Substrate.

As a crucial structural parameter, shell thickness greatly influences the optical properties of metallic nanoshells. However, there still lacks a reliable approach to prepare ultrathin core-shell nanoparticles. To solve this problem, a two-step gold seeding process was pointed out to increase the packing density of gold seeds on the silica core. With use of this method, the packing density of gold seeds reaches ∼60%, enabling us to successfully reduce the shell thickness to the sub-10 nm range. Afterward, we investigated optical properties of the as-prepared ultrathin nanoshells. It is found that thinner nanoshells exhibit a wider optical tunability and a greater electromagnetic field enhancement than their thicker counterparts, which makes ultrathin nanoshells an ideal substrate for surface-enhanced spectroscopes.