Controlling Gold-Assisted Exfoliation of Large-Area MoS2 Monolayers with External Pressure

Gold-assisted exfoliation can fabricate centimeter- or larger-sized monolayers of van der Waals (vdW) semiconductors, which is desirable for their applications in electronic and optoelectronic devices. However, there is still a lack of control over the exfoliation processes and a limited understanding of the atomic-scale mechanisms. Here, we tune the MoS₂-Au interface using controlled external pressure and reveal two atomic-scale prerequisites for successfully producing large-area monolayers of MoS₂. The first is the formation of strong MoS₂-Au interactions to anchor the top MoS₂ monolayer to the Au surface. The second is the integrity of the covalent network of the monolayer, as the majority of the monolayer is non-anchored and relies on the covalent network to be exfoliated from the bulk MoS₂. Applying pressure or using smoother Au films increases the MoS₂-Au interaction, but may cause the covalent network of the MoS₂ monolayer to break due to excessive lateral strain, resulting in nearly zero exfoliation yield. Scanning tunneling microscopy measurements of the MoS₂ monolayer-covered Au show that even the smallest atomic-scale imperfections can disrupt the MoS₂-Au interaction. These findings can be used to develop new strategies for fabricating vdW monolayers through metal-assisted exfoliation, such as in cases involving patterned or non-uniform surfaces.