STEM imaging artifacts with three-fold astigmatism in monolayer transition metal dichalcogenides

Abstract

Aberration-corrected scanning transmission electron microscopy has been demonstrated as a versatile tool to probe the atomic defects and local electronic states in 2D materials. However, the residual aberration of the probe may give rise to considerable deviations from the perfect imaging, especially in polyphase transition metal dichalcogenides. Here, we clarify the misleading imaging artifact of opposite subdomains in monolayer MoS2 through both image simulations and experimental in-plane rotation series. This non-honeycomb imaging artifact turns out to be caused by both probe residual threefold astigmatism and local sample tilt or fluctuation. Our results suggest that the direct STEM imaging should be cautiously treated to achieve accurate phase assignment.