Twisting Dynamics of Large Lattice-Mismatch van der Waals Heterostructures

Abstract

van der Waals (vdW) homo/heterostructures are ideal systems for studying interfacial tribological properties such as structural superlubricity. Previous studies concentrated on the mechanism of translational motion in vdW interfaces. However, detailed mechanisms and general properties of the rotational motion are barely explored. Here, we combine experiments and simulations to reveal the twisting dynamics of the MoS2/graphite heterostructure. Unlike the translational friction falling into the superlubricity regime with no twist angle dependence, the dynamic rotational resistances highly depend on twist angles. Our results show that the periodic rotational resistance force originates from structural potential energy changes during the twisting. The structural potential energy of MoS2/graphite heterostructure increases monotonically from 0° to 30° twist angles, and the estimated relative energy barrier is (1.43 ± 0.36) × 10–3 J/m2. The formation of Moiré superstructures in the graphene layer is the key to controlling the structural potential energy of the MoS2/graphene heterostructure. Our results suggest that in twisting 2D heterostructures, even if the interface sliding friction is negligible, the evolving potential energy change results in a nonvanishing rotational resistance force. The structural change of the heterostructure can be an additional pathway for energy dissipation in the rotational motion, further enhancing the rotational friction force.

Structural Superlubricity of Two-Dimensional Materials: Mechanisms, Properties, Influencing Factors, and Applications

“…However, frictional anisotropy remains almost unchanged [34,68]. The structural potential energy of the graphite and h-BN heterojunction increases monotonically as the twist angle increases from 0 to 30 degrees [69]. The friction between graphene and h-BN follows a stick-slip mechanism based on MD simulations [27].…”

“…With scientific and technological progress, both advanced friction testing techniques and simulation methods are increasingly being used to study structural superlubricity. On the experimental side, for example, the rotational resistance in the relative sliding of graphite flakes was measured using the 'push-edge' and 'drag-center' methods [69] and the morphological structure of graphite contact surfaces after sliding was better characterized using the flip-and-pick (pick-flip technique) [70]. MD simulations and first-principles calculations were used to analyze a series of interlayer frictional dissipation mechanisms.…”