Imaging graphene moir\'e superlattices via scanning Kelvin probe microscopy

TL;DR

This study uses scanning Kelvin probe microscopy to map local surface potentials in twisted double bilayer graphene moiré superlattices, revealing stacking-dependent electronic properties and providing a stable imaging method for domain visualization.

Contribution

It introduces SKPM as a stable technique to distinguish stacking domains in moiré superlattices and correlates surface potential differences with electronic structure variations.

Findings

ABCA domains have ~15 mV higher surface potential than ABAB domains

Surface potential mapping is more stable than LPFM for visualizing moiré patterns

Density functional theory explains work function differences based on stacking

Abstract

Moir\'e superlattices in van der Waals heterostructures are gaining increasing attention because they offer new opportunities to tailor and explore unique electronic phenomena when stacking 2D materials with small twist angles. Here, we reveal local surface potentials associated with stacking domains in twisted double bilayer graphene (TDBG) moir\'e superlattices. Using a combination of both lateral Piezoresponse Force Microscopy (LPFM) and Scanning Kelvin Probe Microscopy (SKPM), we distinguish between Bernal (ABAB) and rhombohedral (ABCA) stacked graphene and directly correlate these stacking configurations with local surface potential. We find that the surface potential of the ABCA domains is ~15 mV higher (smaller work function) than that of the ABAB domains. First-principles calculations based on density functional theory further show that the different work functions between ABCA and ABAB domains arise from the stacking dependent electronic structure. We show that, while the moir\'e superlattice visualized by LPFM can change with time, imaging the surface potential distribution via SKPM appears more stable, enabling the mapping of ABAB and ABCA domains without tip-sample contact-induced effects. Our results provide a new means to visualize and probe local domain stacking in moir\'e superlattices along with its impact on electronic properties.