Scanning\nElectron Microscopy Imaging of Twist Domains\nin Transition Metal Dichalcogenide Heterostructures

Twisted two-dimensional\n(2D) material heterostructures provide\nan exciting platform for investigating fundamental physical phenomena.\nMany of the most interesting behaviors emerge at small twist angles,\nwhere the materials reconstruct to form areas of perfectly stacked\ncrystals separated by partial dislocations. However, understanding\nthe properties of these systems is often impossible without correlative\nimaging of their local reconstructed domain configuration, which exhibits\nrandom variations due to disorder and contamination. In particular,\nvisualization of the local domain configuration allows determination\nof the local twist angle and, hence, the local lattice strain. Here,\nwe demonstrate a simple and widely accessible route to visualize domains\nin the as-produced twisted transition metal dichalcogenide (TMD) heterostructures\nusing electron channeling contrast imaging (ECCI) in scanning electron\nmicroscopy (SEM). This nondestructive approach is compatible with\nconventional substrates and allows domains to be visualized even when\nsealed beneath an encapsulation layer. Complementary theoretical calculations\nreveal how a combination of elastic and inelastic scattering leads\nto contrast inversions at the specified detector scattering angles\nand sample tilts. We demonstrate that optimal domain contrast is therefore\nachieved by maximizing signal collection while avoiding contrast inversion\nconditions.