Investigation of Strain-Localized Excitons in Nanobubbles of Single-Layer WS₂ on a Gold Surface

Solid-state single-photon emitters (SPEs) are crucial for quantum computing and quantum communication applications. Recently, several studies have shown that transition metal dichalcogenide (TMD) based SPEs are promising potential on-demand single-photon sources. To create SPEs in TMD semiconductors, it is essential to locally strain the 2D semiconductor on the nanoscale either with nanopatterned substrates or randomly occurring nanobubbles. In this study, we investigate SPEs in localized nanobubbles of the 2D single-layer (1L) semiconductor tungsten disulfide (WS₂) bound to a pristine gold interface. The gold surface quenches all of the emission from regions that are not strained, providing background-free emission from the nanobubbles. Previous room temperature correlated topographical and power-dependent optical measurements showed that nanobubbles with homogeneous structures host a single emissive state, indicating that the distribution of strain uniformly funnels excitons to a single state. In contrast, low-temperature optical characterization reveals emission from multiple narrow, sharp quantum dot-like states from the same nanobubbles. Current work is focused on performing low-temperature photoluminescence excitation (PLE) spectroscopy that probes the excitonic absorption resonances of the nanobubbles as a function of temperature. Comparison of the absorption and emission resonances at cryogenic temperatures will shed light on the strain distribution inside nanobubbles and provide a quantitative estimate of the binding energy of the highly localized quantum dot-like states inside the nanobubbles. The evolution of these energies as a function of temperature is anticipated to provide insight into how the localization of excitons to quantum dot-like states develops as temperatures decrease. These studies demonstrate how the combination of background-free emission from the nanobubbles and correlated AFM and temperature-dependent optical characterization can provide unique insight into the underlying structure-property relationships of solid-state SPEs in strained 2D semiconductors.