A Novel Route to Surface-Enhanced Raman Scattering: Ag Nanoparticles Embedded in the Nanogaps of a Ag Substrate

An intense surface-enhanced Raman scattering (SERS) effect is realized by depositing Ag nanoparticles (NPs) into the nanogaps of a Ag substrate. The nanogaps are formed by the thermal annealing of a Ag film on a silicon substrate. This SERS substrate has an enhancement factor (EF) of 2.3 x 10(6) and a strong signal enhancement that is 20 times higher than that of substrates without the Ag NPs within the nanogaps. Moreover, the reproducibility is improved with the decreased relative standard deviation of mapping data, which falls from 23.9% down to 12.1%. Its performance is as good as commercial substrates. The electromagnetic distribution between the nanoparticles and nanogaps is simulated by the finite-difference time-domain method, which suggests that the additional enhancement of the SERS effect can be mainly attributed to the remarkable increase of the local electromagnetic field coupling among the Ag NPs, which is at least 12 times higher than that of conventional samples with bare Ag NPs.