Cryogen-free variable-temperature Kelvin probe force microscopy for probing local chemical potential in van der Waals heterostructures.

Abstract

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.