Real-time spatially resolved determination of twist angle in transition metal dichalcogenide heterobilayers

Abstract Two-dimensional (2D) transition metal dichalcogenides (TMDs) offer unique optoelectronic capabilities due to their direct bandgap semiconductor nature in monolayer form. Atomically thin TMDs can be assembled in vertical stacks that are held together by van der Waals forces, enabling interlayer coupling between the layers. This creates new physical properties that depend on the relative orientation (twist angle) between the TMD monolayers. Accurate and fast measurement of the twist angle is therefore of utmost importance for characterizing a 2D TMD heterostructure. Here, we present a nonlinear imaging technique based on second harmonic generation (SHG) microscopy, that enables instantaneous mapping of the twist angle between the two stacked TMD monolayers. By using a polarization beam splitter in the detection path and two detectors measuring two orthogonal SHG polarization components, we acquire with a single-shot measurement the twist angle in a WS ₂ /MoS ₂ heterobilayer, in real time. Remarkably, the twist angle is measured directly in the overlapping region based on a SHG interference model. The demonstrated technique offers a powerful tool for the rapid, all-optical and spatially resolved twist angle determination in large-area 2D TMD heterostructures.