Surface-enhanced Raman spectroscopy based on ordered nanocap arrays

The densely packed two-dimensional arrays of monodisperse polystyrene colloid sphere with 100, 200, 500 and 770nm, were prepared by the self-assembly technique on the Si wafer. Ag nanocaps were fabricated by sputtering system. Then the nanocaps absorbed 4-MPy molecule before test the Raman spectroscopy. The Raman intensity increased with the size of polystyrene colloid sphere decreased. The structure of added Co layer was also systematic investigated [Display omitted] . ► We experimentally demonstrate a SERS enhancement in a two-dimensional ordered array of metal Ag nanocaps. ► To coated Ta layer, we could illustrate that the main contribution of SERS comes from top of Ag nanocaps. ► When added Co in the material and Co layer under Ag film, the Raman intensity would be changed. We fabricated the Ag cap array for surface-enhanced Raman scattering (SERS) by Ag deposition onto two dimensional polystyrene colloid sphere templates, and 4-mercaptopyridine (4-MPy) was used as the probing molecule. When the colloids with different size were chosen as the substrate for 20nm Ag deposition, the film on 100nm colloids gave the significant enhancement. SERS intensity increased with the increase of Ag thickness. When 20nm Ag film was coated by Ta, the SERS signals decreased with the increase of Ta thickness, indicating the main effect from the top of cap structure. When Co layer was added under the Ag film, the SERS intensity decreased with the increase of Co thickness because the Co layer affects electromagnetic and plasmon resonance.