Role of Gap Size and Gap Density of the Plasmonic Random Gold Nanoisland Ensemble for Surface-Enhanced Raman Spectroscopy

Abstract

Surface-enhanced Raman spectroscopy (SERS) using plasmonic effect relies on the amplification of the Raman signals of targeted molecules due to a strong near-field enhancement of plasmonic nanostructures. The SERS intensity, therefore, depends strongly on the geometry of plasmonic structures wherein nanogaps between plasmonic objects play a significant role in the near-field enhancement. Here, using the random gold nanoisland assemble as a plasmonic medium and the Rh6G as the targeted molecule, we show that not only the size of the nanogaps but also their density influence strongly on the SERS intensity. The SERS intensity is found to be significantly improved if the gap size decreases and gap density increases. Our work provides additional information that might be useful for optimizing the SERS signal strength of the random plasmonic media.

Fig. 4 Influence of the AuNP coverage on the SERS intensity. (a) Converted SEM images of the Samples A (a) and Sample B (b) with nearly the same coverage (～60%) together with the FDTD simulations of the distribution of the electromagnetic field over Sample A and Sample B under the excitation of a monochromatic light with wavelength of 632.8 nm, respectively, presented in the same color bar. (c) The comparison of the SERS intensity of Sample A and Sample B. The spectra are shifted in the vertical direction for clarity. The insets show the field enhancement at the typical gaps of Sample A and Sample B, respectively.