Stiffness and Atomic-Scale Friction in Superlubricant MoS₂ Bilayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Two-dimensional (2D) van der Waals heterostructures exhibit unique properties due to weak interlayer interactions.
• Superlubricity, a state of near-zero friction, is crucial for advanced tribological applications.
• Understanding factors influencing superlubricity in 2D materials is essential for designing next-generation devices.

Purpose of the Study:

• To investigate the effect of layer stiffness on the superlubricant state of 2D van der Waals heterostructures.
• To explore the relationship between intralayer stiffness, interlayer sliding energy, and friction.
• To analyze the influence of sliding velocity on friction regimes and temperature distribution.

Main Methods:

• Utilizing molecular dynamics (MD) simulations with *ab initio* machine-learning force fields.
• Engineering bilayers with varying intralayer stiffness but identical interlayer sliding energy surfaces.
• Analyzing friction coefficients and temperature gradients across different sliding velocities.

Main Results:

• A 2-fold increase in intralayer stiffness led to a ~6-fold reduction in friction.
• Two distinct sliding regimes were identified based on sliding velocity.
• At high velocities, significant temperature gradients emerged, dependent on the relative stiffness of the sliding layers.

Conclusions:

• Layer stiffness is a critical parameter controlling superlubricity in 2D van der Waals heterostructures.
• Friction behavior transitions with sliding velocity due to heat exchange dynamics.
• The relative temperature profile between layers is sensitive to material properties and sliding conditions.