Enhanced SERS signal in the hybrid substrate through electronic modulation of CVD grown single-layer graphene

Abstract

The ever-growing demand for sensitive and reliable detection of hazardous material in the food chain and trace detection of chemical entities in a variety of field attracted advanced Surface Enhanced Raman Spectroscopy (SERS) active materials such as graphene-based hybrid SERS. The graphene silver nanostructures (AgNS) based hybrid SERS substrates are explored to understand the critical role of pristine graphene grown by chemical vapor deposition (CVD) on SERS signal and its possible mechanism. A lithography-free fabrication process has been developed for growth of uniform array of AgNS with varying both particle sizes and inter-particle gaps. The optimal AgNS with average feature size ∼40 nm and average inter-particle spacing of ∼13 nm demonstrated the maximum SERS enhancement with rhodamine 6G (R6G). The single-layer graphene (SLG) grown by CVD with the aid of controlling the reaction geometry with growth under a free molecular regime leads to the highest quality graphene with I_2D/I_G ratio of ∼3.58 and I_D/I_G ratio of ∼0.154. The flow regime-controlled CVD-grown SLG integrated with AgNS and its SERS enhancement mechanism is explored for trace detection of R6G. The graphene with its ability to modulate the electronic structure and tune it relative to the highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) levels of R6G molecules resulted in improved SERS signal by about an order for graphene-AgNS hybrid structure as compared to bare AgNS. The obtained findings paved the way for the futuristic and reliable hybrid SERS substrate for trace-level detection of a wide range of chemical entities.