Enhancement of SERS effect in Graphene-Silver hybrids

Surface enhanced Raman spectroscopy (SERS) is considered as one of the most intensively studied analytical technique. Here, Ag nanoparticles (NPs) are coated on graphene layers (GLs) to prepare a hybrid SERS substrate. GLs are known to contribute towards SERS based on chemical enhancement mechanism, and Ag NPs are based on electromagnetic enhancement mechanism. Thus, the synergetic effect of hybrid could be utilized to prepare excellent SERS substrates. Furthermore, effect of Ag NPs with varying size has been studied to check the improvement in SERS. Ten times remarkable enhancement in SERS intensities are observed from the GLs-Ag hybrid as compared to pristine GLs. Density functional theory (DFT) calculations have been carried out through small Ag clusters interaction with graphene fragments to support and understand the mechanism behind the observed phenomena. Strong adsorption of Ag3 cluster on graphene fragment reveals the substantial modification in electronic and vibrational properties of graphene fragment and considerable charge transfer from Ag3 cluster to graphene fragment. Such phenomena further result in G-band’s enhanced intensity in graphene fragment. Our experimental study and theoretical calculations set up basic understanding and open up a way to fabricate the high-performance SERS substrates for proficient sensing applications.