ACS Nano https://doi.org/c7jb (2019)

Interlayer rotation — that is, the degree to which two monolayers are twisted against each other — is commonly observed in the layered structures of 2D materials, resulting in the formation of moiré patterns. Interestingly, even slight rotation variations may have a profound impact on the electronic properties of the resulting material system. However, it is still unclear what governs the formation of different twist angles and whether this process can be controlled to tailor material properties. Now, Zhu and colleagues, using bilayer MoS2 and graphene as model systems, propose a general moiré-driven mechanism to explain the interlayer rotation in 2D layers.

To predict the rotation behaviour, the researchers employ an interface lattice model and molecular dynamics simulations. An interface lattice model — based on the assumption that the relative layer rotation is dominated by interactions of the two atomic layers at the interface — takes into account the relationship between interfacial energy and rotation angle, as well as the effect of the flake size. The analysis shows that the interlayer rotation is driven by the interface lattice moiré, which is universal for any 2D material, regardless of size. Generally, if moiré patterns are formed between two layers with a hexagonal lattice, a triangular array will emerge from the domains with high energy stacking, while a hexagonal array will be formed by the low-energy domains. In both cases, within a finite-sized region, the resulting rotation minimizes the total energy of the domains.