Plasmon-enhanced exciton emissions and Raman scattering of CVD-grown monolayer WS2 on Ag nanoprism arrays

Monolayer transition metal dichalcogenides (TMDs) usually have weak optical emission due to the poor light absorption as being atomically thin. Enhancing their optical properties by surface plasmon resonance is attractive for applying atomically thin TMDs in optoelectronic and photonic devices. Here, Ag/WS2 hybrid structure was fabricated by transferring monolayer WS2 grown via chemical vapor deposition (CVD) onto optimized periodic Ag nanoprism array with well-matched resonance by controlling the mask geometry and etching time of polystyrene (PS) nanospheres. Significant enhanced photoluminescence (PL) emission and Raman scattering were successfully achieved. Especially, the higher enhancement is realized for neutral excitons of monolayer WS2. Theoretical calculations reveal that the plasmonic enhancement mainly results from the highly enhanced local electric field and the charge transfer. This work explores the feasibility of exciton emission and Raman scattering enhancement for TMDs with plasmonic nanostructures fabricated by low-cost and easily-manipulated nanosphere lithography (NSL), which paves a way towards the applications of plasmon-enhanced TMD sensors, emitters, and photodetectors.