Unidirectional van der Waals Monolayer Single Crystals by Deterministic Vicinal Epitaxy

To fully realize the potential of van der Waals (vdW) materials in atomically thin monolayers (MLs), achieving wafer-scale single-crystalline textures with high quality is crucial. Here, we report the realization of unidirectional MoS2 ML single crystals with high quality, achieved through deterministic vicinal epitaxy on vicinal sapphires with patterned SiO2 windows. This was accomplished by modulating the vicinal angle of crystalline miscut sapphire which made the change in unidirectionality and facets. The quality of our MoS2 was identified from the atomic-scale to the circuit-scale through clean atomic surfaces in scanning tunneling microscopy measurements, defect-free photoluminescence similar to that of the exfoliated crystal, and high Hall mobility exceeding 1,200 cm2 V-1 s-1. Centimetre-scale coherent MoS2 single crystalline films were demonstrated by grazing-incidence wide-angle X-ray diffraction. Growth strategies of vicinal epitaxy are applicable to other vdW semiconductors, such as WS2 and WSe2. Our works open up novel routes for the realization of high-quality vdW single crystals, suggesting their potential application as channel materials for quantum electronics and complementary metal-oxide-semiconductor technology.