Exciton-plasmon coupling and giant photoluminescence enhancement in monolayer MoS2 through hierarchically designed TiO2/Au/MoS2 ternary core-shell heterostructure

Enhancing the light coupling efficiency of large-area monolayer molybdenum disulfide (1L-MoS2) is one of the major challenges for its successful applications in optoelectronics and photonics. Herein, we demonstrate a dramatically enhanced photoluminescence (PL) emission from direct chemical vapor deposited monolayer MoS2 on a fluorine-doped TiO2/Au nanoparticle plasmonic substrate, where the PL intensity is enhanced by nearly three orders of magnitude, highest among the reported values. The formation of TiO2/Au/1L-MoS2 ternary core-shell heterojunction is evidenced by the high-resolution transmission electron microscopy and Raman analyses. Localized surface plasmon resonance induced enhanced absorption and improved light coupling in the system was revealed from the UV-vis absorption and Raman spectroscopy analyzes. Our studies reveal that the observed giant PL enhancement in 1L-MoS2 results from two major aspects: firstly, the heavy p-doping of the MoS2 lattice is caused by the transfer of the excess electrons from the MoS2 to TiO2 at the interface, which enhances the neutral exciton emissions and restrains the trion formation. Secondly, the localized surface plasmon in Au NPs underneath the 1L-MoS2 film initiates exciton-plasmon coupling between excitons of the 1L-MoS2 and surface plasmons of the Au NPs at the MoS2/Au interface. The PL and Raman analyses further confirm the p-doping effect. We isolate the contributions of plasmon enhancement from the theoretical calculation of the field enhancement factor using the effective medium approximation of plasmonic heterostructure, which is in excellent agreement with the experimental data. This work paves a way for the rational design of the plasmonic heterostructure for the effective improvement in the light emission efficiency of 1L-MoS2, and may enable engineering the different contributions to enhance the optoelectronic performance of 2D heterostructures.

Automated summary

This study demonstrates a dramatic enhancement of photoluminescence emission from direct chemical vapor deposited monolayer MoS2 on a fluorine-doped TiO2/Au nanoparticle plasmonic substrate, attributing the enhancement to the formation of a TiO2/Au/1L-MoS2 ternary core-shell heterojunction. The enhanced absorption and improved light coupling were revealed through UV-vis absorption and Raman spectra. The observed giant PL enhancement is a result of heavy p-doping of the MoS2 lattice and exciton-plasmon coupling initiated by localized surface plasmons in Au nanoparticles underneath the MoS2 film at the interface.