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Growing continuous monolayer films of transition-metal dichalcogenides (TMDs) without the disruption of grain boundaries is essential to realize the full potential of these materials for future electronics and optoelectronics, but it remains a formidable challenge. It is generally believed that controlling the TMDs orientations on epitaxial substrates stems from matching the atomic registry, symmetry, and penetrable van der Waals forces. Interfacial reconstruction within the exceedingly narrow substrate-epilayer gap has been anticipated. However, its role in the growth mechanism has not been intensively investigated. Here, we report the experimental conformation of an interfacial reconstructed (IR) layer within the substrate-epilayer gap. Such an IR layer profoundly impacts the orientations of nucleating TMDs domains and, thus, affects the materials’ properties. These findings provide deeper insights into the buried interface that could have profound implications for the development of TMD-based electronics and optoelectronics.

Two-dimensional transition metal dichalcogenide nanoribbons are touted as the future extreme device downscaling for advanced logic and memory devices but remain a formidable synthetic challenge. Here, we demonstrate a ledge-directed epitaxy (LDE) of dense arrays of continuous, self-aligned, monolayer and single-crystalline MoS2nanoribbons on β-gallium (iii) oxide (β-Ga2O3) (100) substrates. LDE MoS2nanoribbons have spatial uniformity over a long range and transport characteristics on par with those seen in exfoliated benchmarks. Prototype MoS2-nanoribbon-based field-effect transistors exhibit high on/off ratios of 108and an averaged room temperature electron mobility of 65 cm2V−1s−1. The MoS2nanoribbons can be readily transferred to arbitrary substrates while the underlying β-Ga2O3can be reused after mechanical exfoliation. We further demonstrate LDE as a versatile epitaxy platform for the growth of p-type WSe2nanoribbons and lateral heterostructures made of p-WSe2and n-MoS2nanoribbons for futuristic electronics applications.