Imaging Conductance with Atomic Scale Resolution in van der Waals Heterostructures

Transition metal dichalcogenides (TMDs) are naturally favored for e-beam imaging due to their atomic thickness, semiconducting nature, and heavy atoms that are easy to see under scanning probe techniques. In this project, we use STEM Secondary Electron Beam Induced Current (SEBIC) to image and probe the electrical conductivity and connectivity of the active layers in quantum devices. SEEBIC is an emerging electron microscopy technique for probing the electronic band structure of a material by spatially mapping secondary electrons (SEs) [1,2]. The image signal generated with this technique depends on the device and material parameters including SE generation and emission, work function, and conductivity. The measurement requires special sample preparation and a unique substrate with an electron transparent window for STEM. The method has been initially demonstrated to probe graphene and now it is extended to probe more complex multi-layer Van der Waals (VdW) heterostructures. Our results show that we can distinguish the excitonic and conductive layers and see the WSe2 monolayer with atomic resolution even though it is buried between layers of h-BN and graphene, while regions of h-BN and graphene could be identified using electron energy loss spectroscopy (EELS). The correlation between local atomic structure and the emergent electronic properties is of paramount importance in the design and fabrication of device architectures. The facilitation of direct measurement and visualization of such properties is expected to provide a critical window into the operational physics of devices spanning sensing, optoelectronics, and quantum information processing.<br/><br/>References<br/>[1] Dyck, Ondrej, Jacob L. Swett, Andrew R. Lupini, Jan A. Mol, and Stephen Jesse. "Imaging Secondary Electron Emission from a Single Atomic Layer." Small Methods 5, no. 4 (2021): 2000950<br/>[2] Dyck, Ondrej, Jacob L. Swett, Charalambos Evangeli, Andrew R. Lupini, Jan A. Mol, and Stephen Jesse. "Mapping conductance and switching behavior of graphene devices In situ." Small Methods 6, no. 3 (2022): 2101245