Geometric control of the moire twist angle in heterobilayer flakes

TL;DR

This paper reveals a geometric mechanism that stabilizes specific twist angles in lattice-mismatched 2D heterobilayers, enabling precise control of the moire pattern orientation through edge alignment and strain tuning.

Contribution

It introduces a novel geometric stabilization mechanism for twist angles in heterobilayers, supported by atomistic simulations, advancing control over 2D material heterostructure orientations.

Findings

Robust metastable twist angles at ~0.61° and ~1.89° identified

Energy barriers for locking are significantly larger than for nearby angles

In-plane heterostrain can tune the twist-angle stabilization

Abstract

We demonstrate a finite twist-angle stabilization mechanism in lattice-mismatched 2D heterobilayers, which results from the geometric alignment between the flake edges and its moire pattern. Using atomistic simulations of graphene on hexagonal boron nitride flakes with diameters of up to $\sim 2500${\AA}, we identify robust metastable angles at $\sim 0.61^\circ$ for armchair and $\sim1.89^\circ$ for zigzag-edged flakes, tunable via in-plane heterostrain. This locking mechanism, which relies on energy barriers that are an order of magnitude larger than those of nearby metastable twist angles, provides a geometric route to precision twist-angle control of two-dimensional heterostructures and to understand the self-orientation of macroscopic flakes.