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 (tWTe2) with a twist angle of ∼5°. Despite strong interest in 2D WTe2 systems, little experimental information about their intrinsic microstructure is available, leaving obstacles in modeling their physical properties. The monolayer, and consequently tWTe2, are highly air-sensitive, making it challenging to probe their atomic structures. In this study, we develop a robust method for atomic-resolution visualization of monolayers and tWTe2 obtained through mechanical exfoliation and fabrication. We confirm the high crystalline quality of mechanically exfoliated WTe2 samples and observe that tWTe2 with twist angles of ∼5° and ∼2° retains its pristine moiré structure without substantial deformations or reconstructions. These results provide a structural foundation for future electronic modeling of monolayer and tWTe2 moiré lattices.[1] The successful visualization is achieved through rapid and non-Fickian mass transport of a uniform layer of palladium (Pd) on 2D WTe2 at ∼190 °C.[2] Additionally, the Pd mass transport converts 2D WTe2 into a superconductor, Pd7WTe2, offering a route to design and engineer superconductivity and topological phases.[3]

References:

[1] F. Yuan*, Y. Jia*, G. Cheng, R. Singha, S. Wu, N. Yao, and L. M. Schoop. Atomic resolution imaging of highly air-sensitive monolayer and twisted-bilayer WTe2. Nano Lett., 23(15), 6868-6874 (2023)

[2] Y. Jia*, F. Yuan*, Y. Tang, G. Yu, T. Song, P. Wang, G. Cheng, R. Singha, A. J. Uzan, M. Onyszczak, K. Watanabe, T. Taniguchi, N. Yao, L. M. Schoop, S. Wu. Synthesis of a two-dimensional crystal within a van der Waals gap. Nature Synthesis, 3, 386–393 (2024)

[3] Y. Jia, G. Yu, T. Song, F. Yuan, A. J. Uzan, Y. Tang, P. Wang, R. Singha, M. Onyszczak, Zh. Zheng, K Watanabe, T. Taniguchi, L. M. Schoop, S. Wu. Superconductivity from on- chip metallization on 2D topological chalcogenides. (Accepted by Physical Review X).