Quantifying the strain decay length of thin film stressors on moiré superlattices

The structure and electronic properties of moiré superlattices are sensitively determined by the interlayer twist angle and strain. The twist angle can be controlled by mechanical rotation during stacking, though it frequently shows deviations from the intended angle. Strain, in contrast, is typically uncontrolled during stacking, and introducing intentional and controllable strain has proven more challenging. In this study, we have applied thin film stressors to twisted graphene samples, enabling us to modify the moiré after assembly. Using torsional force microscopy (TFM) to image the moiré with nanometer-scale resolution, we observe that the stressor modifies the period and anisotropy of the moiré. We quantify the strain gradient imparted by the stressor at distances within 50 nm from the stressor edge, providing much greater resolution than diffraction-limited optical techniques. These results demonstrate the feasibility of controlling the symmetry and period of the moirè superlattice following the initial interlayer twist fabrication step, as well as deliberately introducing anisotropy in the moiré, which opens new avenues for engineering electronic structure in moirés.