Probing Heterogeneity in 2D van der Waals Materials via Cryogenic Scanning Transmission Electron Microscopy

Quantum materials exhibit unique phenomena and functionalities that go beyond classical physics. Utilizing 2D sheets and constructing hetero- and moiré structures from them has emerged as a promising method to induce exotic quantum effects. However, studying these materials using cryogenic scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) has historically been limited by stage instability. Recent advancements in stage design by manufacturers now present new opportunities for this line of research. In this talk, I will present our ongoing research using atomic-scale cryogenic STEM and monochromated EELS to investigate the coupling between lattice and electronic structures in several representative 2D van der Waals structures relevant to magnetic storage and spintronic applications. Key examples include the discovery of layer-number-dependent phase transitions in CrCl₃ during cooling, the elucidation of complex local symmetry breaking in the long-wavelength charge density wave material EuAl₄, and the mapping of local excitons in moiré-structured MoTe₂. These studies demonstrate that the electronic and magnetic properties of 2D materials can be tuned by manipulating the layer number or engineering moiré structures. They also highlight the power of combining high-resolution cryogenic STEM imaging and spectroscopy to investigate quantum materials. [1]

[1] This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences, and Engineering Division and performed at the Center for Nanophase Materials Sciences at ORNL.