Tip-Enhanced Dark Exciton Nanoimaging and Local Strain Control in Monolayer WSe2

Dark excitons in transition-metal dichalcogenides, with their long lifetimes and strong binding energies, provide potential platforms from photonic and optoelectronic applications to quantum information science even at room temperature. However, their spatial heterogeneity and sensitivity to strain is not yet understood. Here, we combine tip-enhanced photoluminescence spectroscopy with atomic force induced strain control to nanoimage dark excitons in WSe2 and their response to local strain. Dark exciton emission is facilitated by out-of-plane picocavity Purcell enhancement giving rise to spatially highly localized emission, providing for higher spatial resolution compared to bright exciton nanoimaging. Further, tip???antenna-induced dark exciton emission is enhanced in areas of higher strain associated with bubbles. In addition, active force control shows dark exciton emission to be more sensitive to strain with both compressive and tensile lattice deformation facilitating emission. This interplay between localized strain and Purcell effects provides novel pathways for nanomechanical exciton emission control.

Automated summary

By combining tip-enhanced photoluminescence spectroscopy and atomic force induced strain control, we successfully achieved nanoscale imaging of dark excitons in WSe2 and observed their response to local strain. Dark exciton emission was facilitated by out-of-plane picocavity Purcell enhancement, leading to highly localized emission with higher spatial resolution compared to bright exciton nanoimaging. Furthermore, tip-antenna-induced dark exciton emission was enhanced in areas of higher strain associated with bubbles. Active force control showed that dark exciton emission was more sensitive to strain, with both compressive and tensile lattice deformation facilitating emission. This interplay between localized strain and Purcell effects provides novel pathways for nanomechanical exciton emission control.