Wednesday, December 6
2:00 pm ET/11:00 am PT
The moiré patterns formed upon twisting two layers of an atomically thin material, like graphene, are highly sensitive to the local structure, varying rapidly with variations in twist angle and strain which in turn impact the local electronic band structure. Techniques to visualize moiré superlattices, without perturbing the sample surface, in air, at room temperature are essential to understanding origins of twist disorder, non-uniformity and poor yield in Van der Waals (VdW) heterostructures. In this work, we introduce Torsional Force Microscopy (TFM) as an AFM based technique to image moiré superlattices [1]. TFM relies on driving a torsional resonance in the AFM cantilever and monitoring its response to measure changes in the local friction at the tip-sample interface. In addition to revealing moiré superlattices in twisted bi-layer graphene, TFM was also found to resolve sub-surface moirés as well as atomic lattices of both graphene and hBN. Coupled with a high success rate of over 90% in the samples studied, TFM should enable precise determination of crystallographic orientation of VdW flakes and moiré twist angle and strain for increased control over fabrication of next generation of VdW heterostructures.
[1] M. Pendharkar, et al., arXiv:2308.08814 (2023)
Mihir Pendharkar is a Q-FARM Bloch Postdoctoral Fellow at Stanford University working in the group of David Goldhaber-Gordon focusing on making 2D materials stacking more uniform, reproducible and repeatable. Mihir was previously a postdoctoral researcher at UC Santa Barbara where he also received his PhD and MS in Electrical and Computer Engineering specializing in epitaxy of superconductor-semiconductor heterostructures for applications in topological quantum computation.