Moiré patterns and polytype mapping of epitaxial boron nitride by electron microscopy

Abstract The physical properties of two-dimensional materials are influenced by interlayer twists and the atomic-layer stacking sequences (polytypes), which often coexist in samples grown via metal–organic vapor phase epitaxy (MOVPE). The mixing of different polytypes in thin film makes it challenging to determine whether an observed effect arises from twist angle or polytype. This information is particularly relevant when studying crystal-symmetry-driven phenomena, such as second harmonic generation or piezoelectricity. We present a method which makes use of scanning transmission electron microscopy (STEM) to identify interlayer twist angles and two classes of polytype domains using MOVPE grown boron nitride (BN) as an example. We show that moiré patterns observed in STEM can be used to disentangle interlayer twist and stacking effects on the nanometer scale. This insight is crucial for understanding the macroscopic properties of epitaxial BN layers and for tuning its electronic and optical properties.