Engineered Dielectric Response of Liquid-Filled Interfacial Bubbles in van der Waals Heterostructures

Abstract Interfacial bubbles in van der Waals (vdW) heterostructures are typically regarded as unavoidable byproducts of stacking. Here, we show that they can be repurposed as engineered dielectric nanocavities by intentionally trapping selected liquids during assembly. A simple prewetting step before stamp transfer forms liquid-filled bubbles at hBN/graphite interfaces containing acetone, ethanol, H2O, and NaCl(aq), alongside untreated reference bubbles. Electrostatic force microscopy (EFM), crosstalk correction, and finite-element modeling enable quantitative extraction of the effective dielectric constant (εeff) of individual bubbles, revealing higher εeff for all liquid-filled bubbles than for untreated ones. To estimate the apparent core permittivity of the confined contents, each bubble is modeled as a liquid core enclosed by an hBN shell. Simulations of the tip–bubble–substrate geometry yield core dielectric constants (εcore) larger than εeff yet physically consistent with the trapped media. Acetone and ethanol exhibit εcore values close to their expected dielectric properties, whereas water shows a reduced εcore consistent with nanoconfined pure water. Notably, NaCl(aq) shows a larger εcore than pure water, suggesting distinct electrolyte dielectric behavior under nanoscale confinement. This work establishes vdW bubbles as versatile platforms for engineering local electrostatic functionality and probing confined-liquid dielectric physics in two-dimensional (2D) material assemblies.