Anomalous Room-Temperature Exciton Dynamics in WS2 Nanobubbles Probed by Tip-Enhanced Photoluminescence

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Strain engineering in two-dimensional (2D) transition metal dichalcogenides (TMDCs) offers a powerful approach to modulating their optoelectronic properties, yet understanding localized strain effects at the nanoscale remains challenging. Here, we employ an atomic force microscopy-tip-enhanced photoluminescence (AFM-TEPL) system to investigate room-temperature exciton behavior in monolayer WS 2 nanobubbles formed on graphene substrates. TEPL mapping reveals distinct photoluminescence (PL) distributions, with trion emission dominating at the nanobubble apex, while neutral excitons (X 0 ) accumulate in the edge wrinkle region. Both trion and X 0 peaks exhibit a red-shift from the wrinkle to the apex driven by strain-induced band modulation. Surface potential (SP) and second-order capacitance gradient (CG) measurements indicate that X 0 localization in wrinkles arises from dielectric screening, doping, and funneling effects, whereas piezoelectric field screening at the apex delocalizes electron–hole pairs, reducing the PL intensity. These findings highlight the complex interplay of strain, dielectric environment, and piezoelectric effects in shaping nanoscale excitonic properties. The AFM-TEPL technique proves to be a robust tool for directly probing and visualizing carrier distributions in 2D semiconductors, offering significant potential for advancing research in straintronics, optoelectronics, and beyond, with broad implications for next-generation nanotechnology and flexible device applications.

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