Enhanced Trion Emission from WS2 Monolayers Directly Exfoliated on Ag Nanohole Arrays

Abstract

The extraordinarily large exciton binding energies of transition metal dichalcogenides (TMDs) have attracted significant attention in both fundamental scientific research and innovative technology development. TMD-metal nanostructures have been fabricated to control excitonic behaviors as well as improve the light-matter interaction in TMDs. WS2 monolayers are integrated with periodic Ag nanohole (AgNH) arrays prepared using a template stripping method. The ultrasmooth and contamination-free surface of the template-stripped Ag layer allows for the direct exfoliation of WS2 flakes on the AgNHs. Surface plasmon excitation increases optical absorption in WS2/AgNH, as evidenced by reflectance, PL, and Raman measurements, along with numerical calculations. Furthermore, the AgNH structures significantly increase the trion-to-exciton emission ratios from the WS2 monolayers on them. Nanoscopic surface photovoltage mapping of WS2/AgNH using Kelvin probe force microscopy can visualize electron accumulation at the suspended WS2 region under light illumination, which triggers the formation of trions. All the results highlight the capability of WS2/AgNH to boost trion emission through plasmon-induced concentrated light and a built-in potential gradient. This work introduces a simple and efficient strategy for fabricating TMD-metal integrated systems to control their excitonic behaviors. © 2024 Elsevier B.V.