Atomic Resolution Imaging of Highly Air-Sensitive Monolayer and Twisted-Bilayer WTe2

Bulk Td-WTe2 is a semimetal, while its monolayer counterpart is a two-dimensional (2D) topological insulator. Recently, electronic transport resembling a Luttinger liquid state was found in twisted-bilayer WTe2 (tWTe(2)) with a twist angle of similar to 5 degrees. Despite the strong interest in 2D WTe2 systems, little experimental information is available about their intrinsic microstructure, leaving obstacles in modeling their physical properties. The monolayer, and consequently tWTe(2), are highly air-sensitive, and therefore, probing their atomic structures is difficult. In this study, we develop a robust method for atomic-resolution visualization of monolayers and tWTe(2) obtained through mechanical exfoliation and fabrication. We confirm the high crystalline quality of mechanically exfoliated WTe2 samples and observe that tWTe(2) with twist angles of similar to 5 and similar to 2 degrees retains its pristine moire ' structure without substantial deformations or reconstructions. The results provide a structural foundation for future electronic modeling of monolayer and tWTe(2) moire ' lattices.