Strain-Induced Decoupling Drives Gold-Assisted Exfoliation of Large-Area Monolayer 2D Crystals

TL;DR

This paper uncovers that strain from a gold substrate weakens interlayer coupling in 2D materials, enabling large-area monolayer exfoliation through a strain-induced decoupling mechanism.

Contribution

It reveals the fundamental strain-induced decoupling mechanism behind gold-assisted exfoliation of large-area 2D monolayers, advancing understanding of the process.

Findings

Interlayer coupling is substantially weakened at the gold interface.

Biaxial strain from gold substrate drives the decoupling effect.

Large-area monolayers are produced by preferential cleavage at the weakened interface.

Abstract

Gold assisted exfoliation (GAE) is a groundbreaking mechanical exfoliation technique, producing centimeter scale single crystal monolayers of 2D materials. Such large, high quality films offer unparalleled advantages over the micron sized flakes typically produced by conventional exfoliation techniques, significantly accelerating the research and technological advancements in the field of 2D materials. Despite its wide applications, the fundamental mechanism of GAE remains poorly understood. In this study, using MoS2 on Au as a model system, we employ ultralow frequency Raman spectroscopy to elucidate how the interlayer interactions within MoS2 crystals are impacted by the gold substrate. The results reveal that the coupling at the first interface between the adhered layer on the gold substrate and the adjacent layer, is substantially weakened, with the binding force being reduced to nearly zero. This renders the first interface the weakest point in the system, thereby the crystal preferentially cleaves at this junction, generating large area monolayers with sizes comparable to the parent crystal. Biaxial strain in the adhered layer, induced by the gold substrate, is identified as the driving factor for the decoupling effect. We establish the strain-induced decoupling effect as the primary mechanism of GAE, which could also play a significant role in general mechanical exfoliations.