Negative Friction Coefficients in Superlubric Graphite-Hexagonal Boron Nitride Heterojunctions

Area of Science:

• Materials Science
• Tribology
• Condensed Matter Physics

Background:

• Superlubricity, a state of ultra-low friction, is crucial for advanced mechanical systems.
• Graphite-hexagonal boron nitride (h-BN) heterojunctions are promising materials for tribological applications.
• Understanding friction mechanisms in layered materials is essential for designing efficient interfaces.

Purpose of the Study:

• To investigate the friction behavior of superlubric graphite-h-BN heterojunctions.
• To elucidate the origin of negative friction coefficients observed in these systems.
• To explore the influence of external load and temperature on interfacial friction dynamics.

Main Methods:

• First-principles calculations and molecular dynamics simulations were employed.
• Analysis of moiré superstructure distortions under varying normal loads.
• Investigation of out-of-plane atomic fluctuations at the interface.

Main Results:

• Negative friction coefficients were predicted for graphite-h-BN heterojunctions.
• Load-induced suppression of out-of-plane distortions reduces interfacial dissipation.
• Increased temperature enhances out-of-plane fluctuations, leading to higher friction.

Conclusions:

• The study reveals a novel friction mechanism in layered material heterojunctions.
• This mechanism explains the counterintuitive negative friction and temperature-dependent friction.
• The findings are general and applicable to a wide range of layered material interfaces.