Low Temperature Heating of Silver-Mediated Exfoliation of MoS2

The need for high-quality large-scale monolayers of layered materials pushes the development of scalable gold-mediated exfoliations. Gold proves to be a suitable adhesive for exfoliation of several 2D materials. However, the extension to other noble metals remains underwhelming as gold outperforms all previously studied metals by a large margin. This is attributed to compromised stability against oxidation and surface contamination of less noble metals, leading to nonideal interfaces for exfoliation. The closest competitor to gold is silver, where gold still leads by a factor 100 regarding exfoliated layer size. In this work, a silver-mediated exfoliation process performing on par with gold is presented. The combination of freshly cleaved silver surfaces with a low-temperature annealing is found to be crucial. The exfoliation yield shows a dependence with annealing temperature, leading to loss in exfoliation performance for higher temperature. Raman studies indicate inhomogeneous strain for the MoS2/Ag interface at these temperatures, which hints at the competing factors of thermal activation versus oxidation of silver. Finally, a transfer process is implemented to promote silver to a fully functional exfoliation substrate. Ultimately, heating up exfoliations tips the strict balance between interfacial interactions and surface contaminations toward robust high monolayer yield exfoliation as demonstrated for silver.

Automated summary

This study presents a silver-mediated exfoliation process that rivals gold in performance, showing that a combination of freshly cleaved silver surfaces and low-temperature annealing is crucial. The exfoliation yield is found to depend on annealing temperature, with a loss in performance at higher temperatures. Raman studies indicate inhomogeneous strain at the MoS2/Ag interface at these temperatures.