Mapping Strain and Relaxation in 2D Heterojunctions with Sub-picometer Precision

The electronic, optical, and mechanical properties of two-dimensional (2D) materials are sensitive to, and readily tuned by, strain fields that can be made an order of magnitude larger than in their bulk counterparts. This is especially true in epitaxial lateral heterojunctions, where two different 2D materials seamlessly merge despite a finite lattice mismatch. For small fields of view, geometric phase analysis (GPA) based on atomic-resolution imaging, is able to map the strain field around individual features such as dislocation cores or embedded channels. Fig. 1 shows GPA strain and rotation maps of the sub-nanometer MoS2 channels embedded within a WSe2 monolayer that provide 1D wires in a 2D material [1]. The channels grow from misfit dislocations at the original MoS2/WSe2 interface, and the channel sidewalls are dislocation-free, displaying large uniaxial strain along the channel direction needed for atomic coherence.