A Predictive Model for Monolayer-Selective Metal-Mediated MoS2 Exfoliation Incorporating Electrostatics

The metal-mediated exfoliation (MME) method enables monolayer-selective exfoliation of van der Waals (vdW) crystals, improving the efficacy of large monolayer production. Previous physical models explaining monolayer-selective MME propose that the main contributors to monolayer-selectivity are vdW crystal/metal surface binding energy and/or vdW crystal layer strain resulting from lattice mismatch. However, the performance of some metals for MME is inconsistent with these models. Here, a new model is proposed using MoS2 as a representative vdW crystal. The model explains how the MoS2/metal interface electrostatics, in combination with strain, determines monolayer-selectivity of MME by modulating the MoS2 interlayer energy. Monolayer MoS2/metal interfaces are characterized using in situ Raman spectroscopy and density functional theory calculations to estimate the electrostatics and strain of MoS2 in contact with different metals. The model successfully demonstrates the dependence of MME monolayer-selectivity on the MoS2/metal interface electrostatics and highlights the significance of electrostatics in nanomaterial vdW interactions.