Ultrafast Dynamics of Metal Plasmons Induced by 2D Semiconductor Excitons in Hybrid Nanostructure Arrays

With the advanced progress achieved in the field of nanotechnology, localized surface plasmon resonances are actively considered to improve the efficiency of metal-based photocatalysis, photodetection, and photovoltaics. Here, we report on the exchange of energy and electric charges in a hybrid composed of a two-dimensional tungsten disulfide (2D-WS₂) monolayer and an array of aluminum (Al) nanodisks. Femtosecond pump-probe spectroscopy results indicate that within ∼830 fs after photoexcitation of the 2D-WS₂ semiconductor energy transfer from the 2D-WS₂ excitons excites the plasmons of the Al array. Then, upon the radiative and/or nonradiative damping of these excited plasmons, energy and/or electron transfer back to the 2D-WS₂ semiconductor takes place as indicated by an increase in the reflected probe at the 2D-exciton transition energies at later time delays. This simultaneous exchange of energy and charges between the metal and the 2D-WS₂ semiconductor resulted in an extension of the average lifetime of the 2D-excitons from ∼15 ps to ∼58 ps in the absence and presence of the Al array, respectively. Furthermore, the indirectly excited plasmons were found to live as long as the 2D-WS₂ excitons exist. The demonstrated ability to generate exciton-plasmon coupling in a hybrid nanostructure may open new opportunities for optoelectronic applications such as plasmonic-based photodetection and photocatalysis.