Fig. 1. Monolayer MoS₂ synthesis, characterization, and device fabrication.

a Schematic of cold-wall horizontal reactor setup. b Coalesced monolayer MoS₂ film grown on a 2-inch sapphire substrate using MOCVD at 1000 °C with Mo(CO)₆ and H₂S as precursors. c AFM images at the center and edge of the wafer showing uniform surface coverage, film morphology, and thickness. d In-plane X-ray diffraction showing the epitaxial relation between MoS₂ and sapphire as (10$\overline{1}$0) MoS₂ ‖ (10$\overline{1}$0) α-Al₂O₃. The inset shows a narrow full-width half-maximum (FWHM) of 0.27°, which emphasizes the high crystalline quality of these monolayer films. Raman map of (e) ${\mathrm{E}}_{2g}^1$ and (f) A_1g peaks show <5% variation and the peak separation of 18 cm⁻¹ confirms monolayer MoS₂. g Photoluminescence (PL) map shows an intense peak at 1.84 eV, which is attributed to the indirect to direct bandgap transition in monolayers and is severely suppressed in multilayers of MoS₂. h Schematic and i SEM image of monolayer MoS₂ FET. j Logarithmic scale and k linear scale transfer characteristics of monolayer MoS₂ FET measured at different drain biases (V_D). l Mobility plot and m output characteristics measured at different back gate biases (V_BG).