Strain in 2D TMDCs induced by metal-assisted exfoliation from the polyvinyl alcohol-covered substrate

We have modified the metal-assisted transfer technique to obtain large-area, few-layer flakes from transition metal dichalcogenide bulk crystals by introducing an initial stage—exfoliation of the bulk crystal onto an intermediate substrate, specifically a silicon wafer coated with polyvinyl alcohol. Following this, we thermally evaporate silver onto the sample and transfer the top layers of the crystal along with the silver layer to the target substrate. This technique allows the production of visually non-corrugated single- and few-layer flakes with high yield. A direct comparison of the micro-Raman and micro-photoluminescence spectra of flakes exfoliated using our method with the spectra of those exfoliated from the scotch tape reveals differences in their properties. We identify signatures of deformations in the flakes exfoliated from the intermediate substrate, indicating the presence of static friction between the substrate and the flake. Our findings, thus, suggest a useful method to induce intrinsic deformation in 2D materials.