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

Abstract

The contact strength, adhesion and friction, between graphene and an incommensurate crystalline substrate such as {\it h}-BN depends on their relative alignment angle $\theta$. The well established Novaco-McTague (NM) theory predicts for a monolayer graphene on a hard bulk {\it h}-BN crystal face a small spontaneous misalignment, here ${\theta }_{NM}$\,$\simeq$\,0.45 degrees which if realized would be relevant to a host of electronic properties besides the mechanical ones. Because experimental equilibrium is hard to achieve, we inquire theoretically about alignment or misalignment by simulations based on dependable state-of-the-art interatomic force fields. Surprisingly at first, we find compelling evidence for $\theta =0$, i.e., full energy-driven alignment in the equilibrium state of graphene on {\it h}-BN. Two factors drive this deviation from NM theory. First, graphene is not flat, developing on {\it h}-BN a long-wavelength out-of-plane corrugation. Second, {\it h}-BN is not hard, releasing its contact stress by planar contractions/expansions that accompany the interface moiré structure. Repeated simulations by artificially forcing graphene to keep flat, and {\it h}-BN to keep rigid, indeed yield an equilibrium misalignment similar to ${\theta }_{NM}$ as expected. Subsequent sliding simulations show that friction of graphene on {\it h}-BN, small and essentially independent of misalignments in the artificial frozen state, strongly increases in the more realistic corrugated, strain-modulated, aligned state.

References in corpus (11)

• STM Spectroscopy of ultra-flat graphene on hexagonal boron nitride
• Optimized Tersoff and Brenner empirical potential parameters for lattice dynamics and phonon thermal transport in carbon nanotubes and graphene
• Emergence of Superlattice Dirac Points in Graphene on Hexagonal Boron Nitride
• Commensurate-incommensurate transition for graphene on hexagonal boron nitride
• Assessment of the Thermal Conductivity of BN-C Nanostructures
• Modeling friction: From nanoscale to mesoscale
• Precisely aligned graphene grown on hexagonal boron nitride by catalyst free chemical vapor deposition
• Macroscopic self-reorientation of interacting two-dimensional crystals
• Effect of structural relaxation on the electronic structure of graphene on hexagonal boron nitride
• Static and dynamic friction in sliding colloidal monolayers
• Friction Boosted by Equilibrium Misalignment of Incommensurate Two-Dimensional Colloid Monolayers

Cited by in corpus (6)

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• Exploring the stability of twisted van der Waals heterostructures
• Current trends in the physics of nanoscale friction
• Emerging chirality and moiré dynamics in twisted layered material heterostructures
• Friction of Physisorbed Nanotubes: Rolling or Sliding?
• Simulations of submonolayer Xe on Pt$(111)$: the case for a chaotic low temperature phase