Theory of liquid-mediated strain release in two-dimensional materials

Strain engineering in transition metal dichalcogenides is an important means to manipulate these materials' electronic and optical properties. Recently, it has been shown that WSe2 monolayers grown on fused silica substrates using chemical vapor deposition can retain residual strain due to thermal expansion mismatch. Moreover, it was demonstrated that this strain can be released using a solvent-evaporation mediated decoupling method. A continuum theory to explain these observations is introduced and its predictions analyzed. The theory is used to establish that it is plausible that bonds much weaker than typical covalent bonds are sufficient to stabilize strains in the range of those experimentally observed. It is shown that the presence of the solvent modifies the equilibrium in-plane displacement of the film, while its lifting is negligible. Under the proper conditions, this displacement leads to an increase in the decoupling force, thereby initiating the strain relief process. The theory clarifies the role of the liquid surface tension in the relaxation process, and it identifies the relationships between droplet wetting behavior and initial strain state that will lead to solute-evaporation mediated decoupling.