Edge-Localized Strain in MoS₂ Nanobubbles Resolved at 5 nm by Chemical Imaging and Geometric Mechanics

Two-dimensional transition metal dichalcogenides (TMDs) exhibit remarkable optical and electronic tunability under nanoscale strain and defect engineering. In this work, we employ high-resolution tip-enhanced Raman spectroscopy (TERS) to spatially resolve vibrational and electronic responses from individual nanobubbles in monolayer MoS₂ formed on plasmonic Au substrates. The confined geometry of the nanobubble induces localized strain and curvature, leading to pronounced bandgap modulation and enhanced Raman response. High-resolution TERS mapping reveals strong enhancement and strain-induced frequency shifts with 5 nm spatial precision at cryogenic temperature (78 K). Correlated topographic and spectroscopic imaging enables direct visualization of the interplay between local strain gradients, sulfur vacancy distributions, and near-field plasmonic enhancement. We verified a maximum tensile strain of ∽1.15–1.34% at the nanobubble edge, which gradually diminishes toward the center, yielding a cross-sectional strain profile consistent with a doughnut-shaped distribution. Additionally, to compare with the experimentally estimated strain, we provided geometric mechanistic methods to investigate the average strain of MoS₂ nanobubble. These findings provide new insight into nanoscale structure–property relationships in strained 2D materials and highlight the power of TERS for investigating quantum-confined defects and excitonic phenomena in low-dimensional systems.