Plasmon damping and charge transfer pathways in Au@MoSe2 nanostructures

Hybridization of plasmonic and excitonic elementary excitations provides an efficient mean of enhancing the optical absorption and emission properties of metal/semiconductor nanostructures and is a key concept for the design of novel efficient optoelectronic devices. Here we investigate the optical properties of two-dimensional MoSe 2 quantum well flakes covered with Au nanoparticles supporting plasmonic resonances. Using spatially resolved confocal spectroscopy, we report the observation of a quenching phenomenon of the Raman scattering and photoluminescence emission of both the MoSe 2 layer and the Au nanoparticles. We found that the quenching of the photoluminescence emission from the Au nanoparticles is partial and measurable unlike the one observed for the Au-covered MoSe 2 layers, which is total. Its dependence on the thickness of the MoSe 2 layer is determined experimentally. Based on electrodynamics calculations and on the electronic band alignment at the Au/MoSe 2 interface, the results are interpreted in terms of (1) damping of the plasmonic resonance of the Au nanoparticles due to the optical absorption by the MoSe 2 layer and (2) a two-pathways charge transfer scheme where the photoexcited electrons leak from the MoSe 2 layer to the Au NPs, whereas the photoexcited holes flow in the opposite direction, that is, from the Au NPs to the MoSe 2 layer. The two combined mechanisms account well for the experimental observations and complements the interpretations proposed in the literature for similar metal nanoparticles/transition metal dichalcogenide systems.