Elastocapillary cleaning of twisted bilayer graphene interfaces

Yuan Hou,Zhiping Xu,Zhaohe Dai,Shizhe Feng,Qunyang Li,Luqi Liu,Zhong Zhang,Guorui Wang,Shuai Zhang

doi:10.1038/s41467-021-25302-2

Abstract

Although layered van der Waals (vdW) materials involve vast interface areas that are often subject to contamination, vdW interactions between layers may squeeze interfacial contaminants into nanopockets. More intriguingly, those nanopockets could spontaneously coalesce into larger ones, which are easier to be squeezed out the atomic channels. Such unusual phenomena have been thought of as an Ostwald ripening process that is driven by the capillarity of the confined liquid. The underlying mechanism, however, is unclear as the crucial role played by the sheet’s elasticity has not been previously appreciated. Here, we demonstrate the coalescence of separated nanopockets and propose a cleaning mechanism in which both elastic and capillary forces are at play. We elucidate this mechanism in terms of control of the nanopocket morphology and the coalescence of nanopockets via a mechanical stretch. Besides, we demonstrate that bilayer graphene interfaces excel in self-renewal phenomena.

Highlights

Layered van der Waals materials involve vast interface areas that are often subject to contamination, vdW interactions between layers may squeeze interfacial contaminants into nanopockets
We note that similar configurations have been widely utilized to visualize liquid-phase matters in the field of liquid cell electron microscopy (EM)[26,27]
Unlike EM that is only able to characterize the projected in-plane dimensions, the experimental setup in Fig. 1a allows for the measurement of the three-dimensional geometry of nanopockets via atomic force microscopy (AFM)

Summary

Introduction

Layered van der Waals (vdW) materials involve vast interface areas that are often subject to contamination, vdW interactions between layers may squeeze interfacial contaminants into nanopockets Those nanopockets could spontaneously coalesce into larger ones, which are easier to be squeezed out the atomic channels. Such unusual phenomena have been thought of as an Ostwald ripening process that is driven by the capillarity of the confined liquid. Previous studies have suggested an Ostwald ripening mechanism, which is a process of capillarity-driven mass diffusion from smaller to larger bubbles[19,20,21] This mechanism neglects important aspects of thin sheet elasticity and cannot explain the ripening of remote pockets without substance transport (we shall see shortly). Combining the elasticity of graphene sheet with the capillarity of trapped liquid, we proposed the elastocapillary cleaning mechanism

Methods

Results

Conclusion