Enhancing Light-Matter Interaction in Molybdenum Disulfide Monolayers Using Plasmonic Nanostructures

Two-dimensional transition metal dichalcogenides (2D TMDs) have attracted considerable attention due to their distinctive properties and potential applications in electronics and optoelectronics. Despite their promise, the light absorption efficiency of these materials is hindered by their atomically thin nature, necessitating innovative strategies to enhance and manipulate light-matter interactions. One promising approach involves the use of plasmonic nanostructures, which can amplify and modulate the electromagnetic field in their vicinity, thus enhancing light-matter interactions in 2D TMDs. Molybdenum disulfide monolayer is an example of a 2D TMD compound, considered one of this family's most stable layered materials [1]. It is an inorganic semiconductor with a direct bandgap and high photoluminescence emission, where the optical response is primarily determined by excitonic transitions [1]. In addition, the molybdenum disulfide monolayer exhibits only three first-order Raman active modes [3], being that Second-order bands can also be observed, depending on the excitation energy [4]. In this study, we investigate the vibrational and optical properties of molybdenum disulfide monolayer deposited on gold grating. The grating is composed of long sub-wavelength slits with a width of 100 nm, separated by a periodicity of 1000 nm. We examined the molybdenum disulfide monolayer on both supported and suspended regions inside the grating. Our results show that the molybdenum disulfide monolayer exhibits greater biaxial tensile strain in the regions supported compared to the uniaxial tensile strain observed in the suspended regions within the slits. Furthermore, we find that electron doping in the molybdenum disulfide monolayer within the slits varies with the polarization of the incident radiation. This polarization effect is not observed in the monolayer in direct contact with the Au substrate. This polarization dependence is interpreted in terms of plasmon-induced hot electron injection. It is supported by numerical simulations that indicated localized surface plasmons within the slits for this electric field configuration. Photoluminescence measurements further reveal a polarization-dependent ratio of Trion to A exciton intensity, corroborating the proposed plasmon-induced doping mechanism. These findings contribute to a deeper understanding of the underlying physics in hybrid molybdenum disulfide monolayer on Au nanostructures, offering insights that could advance fundamental plasmonic research and foster future technological applications.<br/>Acknowledgments: <i>This work</i> has been <i>supported</i> by the following <i>Brazilian</i> research <i>agencies</i>:<br/>CAPES (88887.609043/2021-00), CNPQ (380809/2023-0), and FAPESP (2021/03311-3, 2023/11839-3). Also, Swiss National Science Foundation grant (200021L_205114).<br/>References:<br/>[1] Kolobov, V.A, et al., J., Springer Ser. Mater. Sci. 239., (2016).<br/>[2] Lembke, D., et al., ACSNano 6., (2012).<br/>[3] Pimenta, M.A., et al., Acc. Chem. Res. 48.1, (2015).<br/>[4] Li, H. et al., <b>Adv.</b> Funct. Mater. 22.7, (2012).