Mitigating Strain Inhomogeneity in Polycrystalline Molybdenum Disulfide Films via Thermal Relaxation of Polymer Substrates

Polycrystalline two-dimensional (2D) materials yield in-plane strain inhomogeneity due to the residual mismatch accumulated from stitching misoriented grains. Since optoelectronic properties of 2D materials are sensitive to the in-plane strain, characterizing and controlling this strain landscape is key to wafer-scale uniformity. Here, we introduce a polymer-assisted thermal relaxation process that reduces in-plane strain inhomogeneity in polycrystalline monolayer MoS2 films. By heating the polymer substrate above its glass-transition temperature, the MoS2 films on the polymer substrate spontaneously form three-dimensional wrinkles and relieve their strain inhomogeneity. A Raman spectroscopy-based metric is proposed to quantify the strain inhomogeneity in the films across various grain sizes. Finally, we demonstrate that incorporating thermal relaxation into a conventional dry-transfer process reduces strain inhomogeneity by up to 50% relative to as-grown films. This work provides a practical approach to characterize and mitigate strain inhomogeneity in polycrystalline TMDs, enabling homogeneous, wafer-scale 2D films.