Size and Density Control of Au Nanoparticles Decorated on MoS2 Thin Films for Preparing High-Performance SERS Substrates

This study investigates the effect of size and density of decorated Au nanoparticles on the enhancement in the Raman signals of organic molecules. The MoS2/Au SERS substrates with low cost and high sensitivity were prepared to detect Rhodamine 6G dye (R6G) at low concentration. The MoS2 thin films were grown directly on glass substrates (area 1 x 1 cm(2)) using chemical bath deposition. Then, the Au nanoparticles were decorated onto MoS2 thin films via chemical reduction method. The optical, structure and surface morphology properties of MoS2/Au SERS substrates were investigated by UV-Vis spectra, XRD patterns and FESEM images, respectively. The results confirmed that MoS2/Au SERS substrates with a good crystalline structure, uniform distribution and high density of Au NPs on the surface of MoS2 thin films were beneficial to the sensitivity of the SERS signal. The optimal MoS2/Au (80 degrees C, 15 min) SERS substrate showed the average size of the Au NPs of 36 nm, nanogap between Au NPs of 13 nm and presence of porous MoS2 thin film, which combined the synergistic effect of the localized surface-plasmon resonance and charge transfer process for enhancing the SERS signal. The detection sensitivity of SERS substrate is related to (1) the nanogap between Au nanoparticles on the surface of MoS2 thin film (hot spots), (2) the charge transfer process between MoS2/Au interfaces and R6G and (3) the charge transfer process between MoS2 and R6G. The best SERS substrates detected R6G solution at a limit of detection of 10(-14) M and an enhancement factor of 1.76 x 10(13).