Unveiling Atomic Structure and Excitons in Twisted 2D MoTe₂ via Cryogenic STEM-EELS

Moiré heterostructures composed of 2D semiconducting transition metal dichalcogenides (TMDs) have emerged as a rich platform for exploring novel correlated phases [1]. Their physical properties can be precisely tuned through the selection of materials and the manipulation of the twist angle between layers, often leading to the emergence of exotic phenomena. Notable examples include superconductivity [2] and Mott insulating states in graphene [3], and anomalous Hall effect in twisted MoTe₂ [4].<br/> <br/>Twisted MoTe₂ (tMoTe₂), with its distinctive electronic properties, holds potential for applications in topological quantum computing [5]. Electronic, optical, and topological properties of 2D moiré materials are highly sensitive to their underlying atomic structure and lattice reconstruction, which significantly impact their electronic band structure. Therefore, real-space information is essential for applications involving 2D materials, as quantum confinement effects, heterogeneities, defects, and interfaces can profoundly influence and modify the emergent properties.<br/> <br/>In this study, we utilize advanced electron microscopy techniques, combining atomic resolution scanning transmission electron microscopy (STEM) and monochromated electron energy-loss spectroscopy (EELS) at cryogenic temperatures (~100 K), to investigate moiré heterostructures of MoTe₂ with various twist angles. We will discuss interplay between interlayer coupling, excitons, strain, and defects, and their impact on the electronic properties of tMoTe₂, providing insights for future advancements in moiré-based devices. [6]<br/><br/>[1] K.P. Nuckolls & A. Yazdani. Nat Rev Mater (2024) 1–21.<br/>[2] Y. Cao, et al. Nature 556 (2018) 43–50.<br/>[3] Y. Cao, et al. Nature 556 (2018) 80–84.<br/>[4] J. Cai, et al. Nature 622 (2023) 63–68.<br/>[5] R.S.K. Mong, et al. Phys. Rev. X 4 (2014) 011036.<br/>[6] This work was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Microscopy was performed as part of a user proposal at the Center for Nanophase Materials Sciences (CNMS), which is a US DOE Office of Science User Facility at Oak Ridge National Laboratory (ORNL).