Moir\'e patterns and inversion boundaries in graphene/hexagonal boron nitride bilayers

TL;DR

This study uses a phase field crystal model to analyze Moiré patterns and inversion boundaries in graphene/hBN bilayers, revealing how out-of-plane deformations and misorientation angles influence their structure and elastic properties.

Contribution

It introduces a new phase field crystal model incorporating out-of-plane deformations, closely matched to quantum calculations, to study bilayer defects and Moiré pattern transitions.

Findings

Out-of-plane deformations lower inversion boundary energies in hBN.

Coupling creates combined inversion and domain wall defects.

Moiré patterns transition from ordered to smeared with increasing misorientation.

Abstract

In this paper a systematic examination of graphene/hexagonal boron nitride (g/hBN) bilayers is presented, through a recently developed two-dimensional phase field crystal model that incorporates out-of-plane deformations. The system parameters are determined by closely matching the stacking energies and heights of graphene/hBN bilayers to those obtained from existing quantum-mechanical density functional theory calculations. Out-of-plane deformations are shown to reduce the energies of inversion domain boundaries in hBN, and the coupling between graphene and hBN layers leads to a bilayer defect configuration consisting of an inversion boundary in hBN and a domain wall in graphene. Simulations of twisted bilayers reveal the structure, energy, and elastic properties of the corresponding Moir\'e patterns, and show a crossover, as the misorientation angle between the layers increases, from a well-defined hexagonal network of domain boundaries and junctions to smeared-out patterns. The transition occurs when the thickness of domain walls approaches the size of the Moir\'e patterns, and coincides with the peaks in the average von Mises and volumetric stresses of the bilayer.