Torsional Force Microscopy of Van der Waals Moirés and Atomic Lattices

Controlling exotic properties of moiré superlattices in twisted Van der Waals (VdW) materials requires identification of twist angle disorder and strain during their preparation. With individual moiré unit cells varying in size from a few nanometers to few thousand nanometers, techniques that are capable of directly visualizing moiré superlattices across all relevant length scales at experimentally convenient conditions remain scarce. In this work, we introduce AFM based Torsional Force Microscopy (TFM) to visualize moirés in air, at room temperature, on commercially available AFMs, without the need for any electrical contact to the sample or the AFM tip [1]. TFM involves operating the AFM in contact-mode while exciting a torsional resonance of the AFM cantilever; the torsional resonance is sensitive to the local dynamic friction and reproducibly images moirés formed at the graphene-hBN and graphene-graphene interfaces. We observe that subsurface moirés can also be revealed by increasing the vertical loading force on the AFM tip. Additionally, atomic lattices of graphene and hBN are also observed, enabling precise determination of crystallographic orientation of flakes.

[1] M. Pendharkar, et al., preprint arXiv:2308.08814 (2023)

*US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract DE-AC02- 76SF00515. SLAC National Accelerator Laboratory, Q-BALMS Laboratory Directed Research and Development. National Science Foundation ECCS-2026822. Gordon and Betty Moore Foundation GBMF9460. JSPS KAKENHI (Grant Numbers 21H05233 and 23H02052) and World Premier International Research Center Initiative (WPI), MEXT, Japan.

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Bulletin of the American Physical Society

2024 APS March Meeting

Monday–Friday, March 4–8, 2024; Minneapolis & Virtual

Session S64: Characterizations of 2D Materials by Photoemission and Scanning Probe

Abstract: S64.00010 : Torsional Force Microscopy of Van der Waals Moirés and Atomic Lattices*

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