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

ABSTRACT

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.