Insights on the enhanced Raman scattering of monolayer TMDCs (Mo, W)(S, Se)2 with Ag nanoparticles via rapid thermal annealing

Abstract

Light interactions between metallic nanostructures and ultra-thin two-dimensional transition metal dichalcogenides (TMDCs) exhibit unique physical properties that are promising for fundamental interests and technological applications. Herein, we successfully demonstrate that self-assembled Ag nanoparticles fabricated by a rapid thermal annealing (RTA) process at certain temperature can be hybridized on systematical monolayer (ML) TMDC (Mo, W)(S, Se)2 surfaces. The morphologies, diameters, and heights of RTA-formed Ag nanoparticles on ML TMDCs are estimated from a statistical perspective. The optical properties of four pristine ML (MoS2, WS2, MoSe2, WSe2) triangular flakes and their corresponding hybrid Ag-ML TMDC nanostructures are comprehensively studied by high-resolution laser confocal micro-Raman spectroscopy. It is found that significant enhancement of typical E2g1 and A1g active modes of Raman scattering in the four ML TMDCs is achieved by integrating self-assembled Ag plasmonic nanoparticles, resulting from a localized surface plasmon resonance (LSPR) at the boundaries of the hybrid nanocomposites. The underlying regime of plasmonic resonance between self-assembled Ag nanoparticles and ML TMDCs can be categorized as weak plasmon-exciton coupling, which has been demonstrated by more detailed physical simulations based on the finite-difference time-domain (FDTD) method.