Controlling twist angle and strain in van der Waals heterostructures

In the low twist angle limit for bilayer graphene, reconstruction of the moiré superlattice leads to strain and twist angle inhomogeneities [1]. While strain is ubiquitous, its influence on the resulting bandstructure remains poorly understood and prevents reliable fabrication of such heterostructures as well as the observation of correlated states for twist angles lower than 1.1° as the bandstructures varies widely with smal perturbations of the moiré unit cell [2].

Here, we demonstrate a novel fabrication method that addresses these questions by using the tip of an atomic force microscope to mechanically bend graphene ribbons on various substrates, thus continuously and homogeneously varying both twist angle and strain. We confirm through piezo force microscopy and Raman spectroscopy that our technique allows for a continuous and independent variation of both twist angle and strain within a single device. Finally, we show this technique can be applied to any vdW materials, limited only by material stiffness.

[1] S. Dai et al. Nano Lett.16, 5923-5927 (2016)

[2] Z. Bi et al. Phys. Rev. B 100, 035448 (2019)