Strain-Induced Decoupling Drives Gold-Assisted Exfoliation of Large 2D Crystal Monolayers

Among fabrication techniques for two-dimensional (2D) materials, mechanical exfoliation is recognized for producing films of the highest quality. However, only at small sizes and without monolayer selectivity. Gold-assisted exfoliation (GAE) is a groundbreaking mechanical exfoliation technique, enabling the production of centimeter-scale single-crystal monolayers, limited only by the size of parent crystals [1]. The method significantly expands exfoliated film area by several orders of magnitude compared to conventional exfoliation methods. Such large, high-quality films offer unparalleled advantages for research and technological advancement and have been instrumental to the construction of a wide variety of structures including free-standing monolayers, large heterostructures and moiré superlattices.

Despite extensive use and significant impact, the fundamental mechanism of GAE is still unclear. In this study, using MoS₂ on Au as a model system, we employ ultra-low frequency Raman spectroscopy to elucidate the interlayer interactions within MoS₂ crystals and reveal the impact of gold exfoliating substrates. We find that gold substrates weaken the coupling between the adhered MoS₂ layer and other layers. For crystals thicker than five layers, coupling at this interface is reduced to almost zero, rendering it the weakest of the system. During exfoliation the crystal preferentially cleaves at this junction, generating large monolayers with sizes comparable to the parent crystal [2].

Biaxial strain, induced by gold in the adhered layer, is identified as the driving factor for the decoupling effect. Density functional theory (DFT) simulations reveal that when both biaxial strain and the crystal thickness exceed specific thresholds, monolayer exfoliation becomes energetically favorable. We thereby establish the strain-induced decoupling effect as the primary mechanism of GAE, which could also play a significant role in general mechanical exfoliations.


[1] Velický, M. et al, Mechanism of Gold-Assisted Exfoliation of Centimeter-Sized Transition-Metal Dichalcogenide Monolayers. ACS Nano 2018, 12, 10463–10472.
[2] Ziewer, J. et al, Strain-induced decoupling drives gold-assisted exfoliation of large-area monolayer 2D crystals, arxiv.org/pdf/2412.05898.