Wafer-scale MoSe₂ single crystals. (A) Photograph of 2-inch monolayer MoSe₂ single-crystal film on C/A-1° sapphire substrate. (B) Optical microscopy image showing the cleanness, uniformity, and continuity of the as-grown MoSe₂ film. A scratch was made for the optical contrast. (C, D) Raman and PL line scans across a 2-inch MoSe₂ single-crystal film. (E) AFM height image of as-grown MoSe₂ film, displaying a clean and wrinkle-free surface. (F) SHG mapping over 100 μm×100 μm, revealing the single-crystal feature of the as-grown MoSe₂ film. (G, H) Statistical distributions of the Raman and PL peak position from three mapping zones (16875 Raman spectra, 10800 PL spectra).