Ferroelectric properties of bilayer MoS₂/WS₂ heterostructure modulated by twist angle

Abstract

The emergence of sliding ferroelectricity is found in non-ferroelectric two-dimensional materials, which brings novel ferroelectric phenomena and expands the potential for advancing ferroelectric devices. Experimental studies have largely focused on sliding ferroelectricity with fixed twist angles owing to the limitations of preparation methods with controlled angles. However, how to modulate the ferroelectric properties in the sliding materials is still challenging. In this work, the out-of-plane ferroelectric properties of typical bilayer MoS2/WS2 heterostructure are reported by precisely controlling twist angles. The experimental results demonstrate that the second-harmonic generation response, indicative of symmetry breaking, decreases as the twist angle increases. In addition, the switching voltage of ferroelectric polarization exhibits the opposite trend with increasing the twist angle. According to experimental studies and theoretical calculations, the tunability of ferroelectric properties arises from the distortion of polar symmetry regions induced by Moiré patterns at different twist angles. Furthermore, the ferroelectric semiconductor field-effect transistors yield the twist angles dependent electrical properties, achieving a large ferroelectric memory window of ≈14 V. The study opens the door to significantly modulating the sliding ferroelectricity via designing twist angles, which will enrich the framework of twistronics and expand the promising applications in the emerging sliding ferroelectric devices.