Electromagnetic Enhancement in Shell-Isolated Nanoparticle-Enhanced Raman Scattering from Gold Flat Surfaces

The electromagnetic (EM) enhancement in shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was systematically analyzed for the first time by using the three-dimensional finite difference time domain (3D-FDTD) method. Compared with a bare metallic nanoparticle directly contact to a gold flat surface, a hot spot with stronger EM enhancement occurs in the junction between silica shell-isolated nanoparticle and flat surface in SHINERS. The largest enhancement factors can be as high as 9 orders of magnitude. The exact locations of hot spots and their EM enhancement strongly depend on the thickness of the silica shell, with an optimal thickness of 1 or 2 nm under 633 nm laser excitation. The dependence of the EM enhancement on both particle size and silica shell thickness was also investigated. The results further demonstrate that the SHINERS should be useful as a general diagnostic tool for surface science.