Local strain-engineering of exciton energy in 2D materials with nanoindentation

Localized strain has emerged as a key parameter in locally tuning the electronic properties of 2D materials, including its role as a factor in the formation of single-photon emitters in 2D transition-metal dichalcogenides. While multiple studies have demonstrated the importance of localized strain, a quantitative understanding of how strain influences these optoelectronic phenomena and their properties remains incomplete, largely due to the lack of experimental approaches capable of applying large, well defined, localized strains. Here, we demonstrate that nanoindentation with spherical atomic force microscopy tips on polymer-supported 2D WSe₂ enables controlled application of large, local strain fields. Far-field photoluminescence spectroscopy reveals exciton energy red shifts of up to 0.29 eV, corresponding to maximum strains of 2.7% in the indent center, assuming -0.109 eV shift per % strain. By varying the indent depth, we achieve control over the strain magnitude, and by changing the spherical tip radius, we scale the spatial extent of the strained region. Combined with the deterministic positioning capability of atomic force microscopy, this method provides a precise and versatile platform for studying strain-dependent phenomena in 2D materials.