Namkyung Lee

Moiré patterns arising from twisted van der Waals stacks fundamentally reshape their electronic properties, enabling band structure engineering that has driven rapidly growing interest in this field. In studying electronic properties, however, structural disorder present in real devices often leads to twist-angle inhomogeneity and obscures angle-dependent electronic effects when measured with bulk-averaged measurements. Probes that can access the local thermodynamic response of the electronic systems with high sensitivity would be highly valuable. Here, we adopt Kelvin probe force microscopy to locally investigate graphene–hBN superlattices. By additionally modulating the chemical potential of the system, we obtain the inverse compressibility with a high signal-to-noise ratio, enabling extraction of the local thermodynamic DOS. From this information, we determine the local twist angle along the device and find that twist-angle deviations are strongly correlated with bubble-induced strain features. Furthermore, by simultaneously tracking the offsets in the contact potential difference and in the net charge, we identify which interface within the heterostructure hosts the trapped bubbles. This capability to identify local electro-chemical environments provides a practical tool for strain-based studies and future device designs utilizing nanoscale engineering in moiré systems.

We report the development of a variable-temperature Kelvin probe force microscopy (KPFM) system based on a Gifford–McMahon cryocooler, which enables stable and highly sensitive operation across a broad temperature range. The system integrates a custom-designed phase-locked loop, automatic gain control, and compact passive vibration isolation stages, effectively suppressing mechanical vibrations intrinsic to cryostats. We demonstrate the system’s performance using a monolayer graphene (MLG) device encapsulated in hexagonal boron nitride, serving as a benchmark platform to validate spatial resolution and CPD sensitivity. Despite the presence of a dielectric encapsulation layer, our system achieves high CPD sensitivity. Temperature-dependent measurements further confirm the capability to resolve subtle changes in chemical potential near the charge neutrality point, consistent with the known electronic structure of MLG. This work establishes a variable temperature KPFM platform suitable for investigating temperature-dependent quantum electronic phases in van der Waals heterostructures.