Graphene on h-BN: to align or not to align?

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• The interaction between graphene and hexagonal boron nitride (h-BN) is crucial for electronic and mechanical applications.
• The Novaco-McTague (NM) theory predicts a specific misalignment angle between graphene and h-BN.
• Achieving true equilibrium states experimentally is challenging, necessitating theoretical investigation.

Purpose of the Study:

• To theoretically investigate the equilibrium alignment and misalignment of graphene on h-BN.
• To understand the factors causing deviations from the established Novaco-McTague theory.
• To analyze the impact of alignment on the frictional properties between graphene and h-BN.

Main Methods:

• Utilized state-of-the-art interatomic force fields for theoretical simulations.
• Performed simulations to model the equilibrium state of graphene on h-BN.
• Conducted comparative simulations with artificially constrained flat graphene and rigid h-BN.

Main Results:

• Found compelling evidence for complete energy-driven alignment (θ = 0) in the equilibrium state.
• Identified two key factors deviating from NM theory: graphene corrugation and h-BN substrate relaxation.
• Simulations with constrained flat graphene and rigid h-BN reproduced the predicted misalignment.

Conclusions:

• Graphene and h-BN exhibit full alignment at equilibrium, driven by substrate relaxation and graphene corrugation.
• Friction between graphene and h-BN significantly increases in the realistic corrugated and strain-modulated aligned state.
• These findings challenge existing theories and highlight the importance of realistic interface dynamics for material properties.