Twist Angle Dependent Strain Distribution in Stacked Transition Metal Dichalcogenide and Charge Density Mapping

Stacking angle control in van der Waals layer assembly has enabled engineering moire superlattices with the tunable length scale. More importantly, interplay between intralayer and interlayer interaction induces periodic atomic modulation at the interface, creating commensurate domains and domain boundaries. We note that the domain boundaries can host emergent functionalities which is associated with the atomic displacement that occurs during the interface reconstruction process. For instance, recent theoretical investigation suggests that piezoelectricity can be induced along the domain boundaries in the twisted bilayer transition metal dichalcogenides. This attracts attention to the twisted bilayer transition metal dichalcogenides structure because of its potential application to low dimensional devices. However, magnitude as well as spatial distribution of strain in the domain wall depending on rotation angle, and atomic scale understanding of charge distribution in the domain boundary still needs progress.<br/>In this study, we performed atomic scale structural investigation on the twisted bilayer transition metal dichalcogenides using aberration corrected scanning transmission electron microscopy (STEM). We measured the magnitudes of induced strain near the domain boundaries of reconstructed bilayers with varying stacking angle. We further analyzed internal electric field, and charge distribution in the reconstructed domains and domain walls with STEM. Our work elucidates the role of stacking angle on structural deformation and emergent functionalities induced by local atomic rearrangement that sensitively depends on the stacking angle.