Towards systematic twist angle control and moiré uniformity in twisted vdW heterostructures

A variety of correlated electronic phases emerge at special ‘magic’ values of interlayer twist angles in graphene moiré systems, where electronic structure is highly sensitive to this twist. However, exploration of the underlying physics has been limited by an inability to achieve a precise twist angle uniformly across a sample and repeatably in different samples.

Here, we present a novel strategy for stacking twisted bilayer graphene by supporting each graphene with BN to minimize the local lattice dynamics that often lead to spatial inhomogeneities and deviations from target twist angle. Using torsional force microscopy (TFM) [1, 2] to directly image the moiré superlattice, we characterize its spatial variations over microns to compare typical moiré disorder in graphene-graphene systems versus graphene-on-BN. We demonstrate the ability to systematically align vdW flakes that originate from different crystals – as opposed to the ‘tear-and-stack’ method commonly used to assemble twisted homolayers [3]. Finally, we present preliminary transport data to quantify the accuracy and uniformity of the final twist angle achieved with this new strategy.

[1] Pendharkar et al. Torsional force microscopy of van der Waals moirés and atomic lattices. PNAS 121 (10) 2314083121 (2024)

[2] Tran, Uslu et al. Quantitative determination of twist angle and strain in Van der Waals moiré superlattices. Appl Phys Lett 125, 113106 (2024)

[3] Kamat, Sharpe et al. Deterministic fabrication of graphene hexagonal boron nitride moiré superlattices. PNAS 121 (40) 2410993121