Breakdown of self-cleaning mechanism for nanoscale interfacial substances in tiny-angle twisted bilayer graphene

TL;DR

This study investigates how the self-cleaning mechanism in twisted bilayer graphene breaks down at nanoscale, revealing the influence of moiré superlattice on interfacial bubble motion and stability.

Contribution

It demonstrates the breakdown of the self-cleaning mechanism at nanoscale in tiny-angle twisted bilayer graphene and links bubble behavior to the moiré superlattice structure.

Findings

Bubbles move along domain boundaries when comparable to AA-stacking regions.

Bubbles become fixed in AA-stacking regions when smaller than these regions.

The moiré superlattice significantly affects nanoscale interfacial substance motion.

Abstract

Realization of high-quality van der Waals (vdW) heterostructures with tailored properties by stacking two-dimensional (2D) layers requires atomically clean interfaces. Because of strong adhesion between the constituent layers, the vdW forces could drive trapped contaminants together into submicron-size bubbles, which leaves large interfacial areas atomically clean. Such a phenomenon is dubbed self-cleaning mechanism in 2D systems. Here, we demonstrate the breakdown of self-cleaning mechanism for nanoscale interfacial bubbles in tiny-angle twisted bilayer graphene (TBG). In the tiny-angle TBG, there is a triangular network of domain boundaries due to structural reconstruction. Our experiments indicate that the bubbles will mainly move along the triangular network of domain boundaries when the sizes of the bubbles are comparable to that of an AA-stacking region in the TBG. When the size of the bubble is smaller than that of an AA-stacking region, the bubble becomes motionless and is fixed in the AA-stacking region because of its large out-of-plane corrugation. Our results reveal a substantial influence of the moir\'e superlattice on the motion of nanoscale interfacial substances.