Dielectric Constant in Nanoscale Bubbles on MoS₂

Nanoscale bubbles form inevitably during the transfer of two-dimensional (2D) materials on a target substrate due to their van der Waals interaction. Despite a large number of studies based on nanobubble structures with localized strain, the dielectric constant (kappa) in nanobubbles of MoS2 is poorly understood. Here, we report kappa measurements for nanobubbles on MoS2 by probing the polarization forces based on electrostatic force microscopy. Remarkably, higher kappa values of 6-8 independent of the nanobubble size are observed for the nanobubbles as compared to flat regions with a kappa of approximate to 3. We find that the charge carrier increase owing to the strain-induced bandgap reduction is responsible for the enhanced kappa of the nanobubbles, where the measured kappa is in good agreement with the calculations based on the Clausius-Mossotti relation. Our results provide fundamental information about the strain-induced local dielectric properties of 2D materials and a guide for the design and fabrication of high-performance optoelectrical devices based on 2D materials.