3D Nanostructures of Silver Nanoparticle-Decorated Suspended Graphene for SERS Detection

The silver nanoparticle-decorated suspended graphene was proposed and fabricated to increase the efficiency of surface-enhanced Raman scattering (SERS) mainly by the enhanced electric field resulting from exciting the localized surface plasmon resonance. The morphology of cavity under the graphene was controlled by the thickness of catalyst and the etching time in the metal-assisted chemical etching process (MacEtch). The reflectance and ellipsometric spectra were examined to understand the optical behaviors of silver nanoparticle-decorated suspended graphene as functions of the etching time. For the samples treated with MacEtch, the Raman signals of graphene and p-mercaptoaniline were greatly enhanced due to the plasmonic cavity effect. Moreover, the graphene could increase the Raman intensity of the probed molecules by chemical enhancement. With the optimal etching time of 15 s, the SERS signals reached the maximum that was 13–15 times larger than those without etching. The electric field enhancement profiles and the SERS enhancement factor were simulated by finite-difference time-domain method to characterize the field distribution around the silver nanoparticles and to verify the enhanced SERS phenomenon observed in measurements.