Ultrahigh Raman Enhancement on Monolayer MoS2

Abstract

Surface-enhanced Raman scattering (SERS) is commonly associated with noble metal substrates. However, over the years modest Raman enhancements (<104) have also been observed in semiconductor substrates. This enhancement stems predominantly from the excitonic resonance of the semiconductors. The use of two-dimensional semiconductors with large excitonic oscillator strength provides an attractive pathway to further enhance this effect. Here we report for the first time a >3 × 105 enhancement in SERS signal from an organic molecule (4-mercaptopyridine) placed in the near field of a two-dimensional semiconductor molybdenum disulfide (MoS2) monolayer. This large enhancement in the SERS signal is attributed to the charge transfer (CT) state formed at the interface of the 2D semiconductor and organic molecule and is found to occur when the excitation source is chosen to be in resonance with the CT state. This approach provides a new strategy for carrying out SERS experiments on molecules with very weak Raman signatures without the need for nanopatterning.